Image signal encoding/decoding method, and apparatus therefor

ABSTRACT

An image decoding method according to the present invention comprises the steps of: deriving a merge candidate of a current block from a neighboring block of the current block; adding the derived merge candidate to a merge candidate list; when the number of merge candidates previously added to the merge candidate list is less than a threshold value, adding at least one prediction area merge candidate included in a prediction area motion information table to the merge candidate list; deriving motion information about the current block on the basis of the merge candidate list; and performing motion compensation on the current block on the basis of the derived motion information.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/224,720 filed Apr. 29, 2021, which is a continuation of InternationalApplication No. PCT/KR2019/015199, filed on Nov. 8, 2019, and entitled“IMAGE SIGNAL ENCODING/DECODING METHOD AND APPARATUS THEREOF”, which isbased on and claims priorities of Korean Application No.10-2018-0136308, filed on Nov. 8, 2018 and Korean Application No.10-2018-0148874, filed on Nov. 27, 2018. The disclosure of the aboveapplications is hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to a video signal encoding and decodingmethod and an apparatus therefor.

BACKGROUND

As display panels are getting bigger and bigger, video services offurther higher quality are required more and more. The biggest problemof high-definition video services is significant increase in datavolume, and to solve this problem, studies for improving the videocompression rate are actively conducted. As a representative example,the Motion Picture Experts Group (MPEG) and the Video Coding ExpertsGroup (VCEG) under the International TelecommunicationUnion-Telecommunication (ITU-T) have formed the Joint Collaborative Teamon Video Coding (JCT-VC) in 2009. The JCT-VC has proposed HighEfficiency Video Coding (HEVC), which is a video compression standardhaving a compression performance about twice as high as the compressionperformance of H.264/AVC, and it is approved as a standard on Jan. 25,2013. With rapid advancement in the high-definition video services,performance of the HEVC gradually reveals its limitations.

SUMMARY

An object of the present disclosure is to provide a method of deriving amerge candidate using a prediction region motion information list and anapparatus for performing the method, in encoding/decoding a videosignal.

Another object of the present disclosure is to provide a redundancycheck method of checking redundancy between a prediction region mergecandidate included in a prediction region motion information list and amerge candidate included in a merge candidate list, in encoding/decodinga video signal.

Another object of the present disclosure is to provide a method ofderiving merge candidates of blocks included in a merge processing areaand an apparatus for performing the method, in encoding/decoding a videosignal.

The technical problems to be achieved in the present disclosure are notlimited to the technical problems mentioned above, and unmentioned otherproblems may be clearly understood by those skilled in the art from thefollowing description.

A method of decoding and encoding a video signal according to thepresent disclosure includes the steps of: deriving a merge candidate fora current block from a neighboring block of the current block; addingthe derived merge candidate to a merge candidate list; adding at leastone prediction region merge candidate included in a prediction regionmotion information list to the merge candidate list when the number ofmerge candidates added to the merge candidate list is smaller than athreshold value; deriving motion information for the current block basedon the merge candidate list; and performing motion compensation for thecurrent block based on the derived motion information. At this point,whether to add the prediction region merge candidate to the mergecandidate list may be determined based on a result of comparison betweenmotion information of the prediction region merge candidate and motioninformation of a merge candidate included in the merge candidate list.

In the method of decoding and encoding a video signal according to thepresent disclosure, the comparison may be performed on at least onemerge candidate in the merge candidate list, of which an index issmaller than or equal to a threshold value.

In the method of decoding and encoding a video signal according to thepresent disclosure, the comparison may be performed on at least oneamong a merge candidate derived from a left neighboring block positionedon a left side of the current block and a merge candidate derived from atop neighboring block positioned on a top of the current block.

In the method of decoding and encoding a video signal according to thepresent disclosure, when it is determined that there is a mergecandidate having motion information the same as that of a firstprediction region merge candidate in the merge candidate list, the firstprediction region merge candidate is not added to the merge candidatelist, and whether to add to a second prediction region merge candidateto the merge candidate list may be determined based on a result ofcomparison between motion information of the second prediction regionmerge candidate included in the prediction region motion informationlist and motion information of the merge candidate included in the mergecandidate list.

In the method of decoding and encoding a video signal according to thepresent disclosure, determination on whether the second predictionregion merge candidate has motion information the same as that of amerge candidate having motion information the same as that of the firstprediction region merge candidate may be omitted.

In the method of decoding and encoding a video signal according to thepresent disclosure, a difference between the number of prediction regionmerge candidates included in the prediction region merge candidate listand an index of the prediction region merge candidate may be smallerthan or equal to a threshold value.

The method of decoding and encoding a video signal according to thepresent disclosure may further include the step of adding a currentinter-region merge candidate derived based on motion information of thecurrent block to the inter-region motion information list. At thispoint, when there is a prediction region merge candidate the same as thecurrent prediction region merge candidate, the prediction region mergecandidate the same as the current prediction region merge candidate maybe deleted, and a largest index may be assigned to the currentprediction region merge candidate.

Features briefly summarized above with respect to the present disclosureare merely exemplary aspects of the detailed description of the presentdisclosure that will be described below, and do not limit the scope ofthe present disclosure.

According to the present disclosure, inter prediction efficiency can beimproved by providing a method of deriving a merge candidate using aprediction region motion information list.

According to the present disclosure, inter prediction efficiency can beimproved by simplifying the redundancy check between a prediction regionmerge candidate and a merge candidate.

According to the present disclosure, inter prediction efficiency can beimproved by providing a method of deriving merge candidates of blocksincluded in a merge processing area.

The effects that can be obtained from the present disclosure are notlimited to the effects mentioned above, and unmentioned other effectsmay be clearly understood by those skilled in the art from the followingdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a video encoder according to anembodiment of the present disclosure.

FIG. 2 is a block diagram showing a video decoder according to anembodiment of the present disclosure.

FIG. 3 is a view showing a basic coding tree unit according to anembodiment of the present disclosure.

FIG. 4 is a view showing various partition types of a coding block.

FIG. 5 is a view showing a partitioning pattern of a coding tree unit.

FIG. 6 is a flowchart showing an inter prediction method according to anembodiment of the present disclosure.

FIG. 7 is a view showing a nonlinear motion of an object.

FIG. 8 is a flowchart showing an inter prediction method based on anaffine motion according to an embodiment of the present disclosure.

FIG. 9 is a view showing an example of affine seed vectors of eachaffine motion model.

FIG. 10 is a view showing an example of affine vectors of subblocks in a4-parameter motion model.

FIG. 11 is a flowchart showing a process of deriving motion informationof a current block using a merge mode.

FIG. 12 is a view showing an example of candidate blocks used forderiving a merge candidate.

FIG. 13 is a view showing positions of reference samples.

FIG. 14 is a view showing an example of candidate blocks used forderiving a merge candidate.

FIG. 15 is a view showing an example in which the position of areference sample is changed.

FIG. 16 is a view showing an example in which the position of areference sample is changed.

FIG. 17 is a flowchart showing a process of updating a prediction regionmotion information list.

FIG. 18 is a view showing an embodiment of updating a prediction regionmerge candidate list.

FIG. 19 is a view showing an example in which an index of a previouslystored prediction region merge candidate is updated.

FIG. 20 is a view showing the position of a representative subblock.

FIG. 21 is a view showing an example in which a prediction region motioninformation list is generated for each inter prediction mode.

FIG. 22 is a view showing an example in which a prediction region mergecandidate included in a long-term motion information list is added to amerge candidate list.

FIG. 23 is a view showing an example in which a redundancy check isperformed only on some of merge candidates.

FIG. 24 is a view showing an example in which a redundancy check isomitted for a specific merge candidate.

FIG. 25 is a view showing an example in which candidate blocks includedin the same merge processing area as the current block are set to beunavailable as a merge candidate.

FIG. 26 is a view showing a temporary motion information list.

FIG. 27 is a view showing an example of merging a prediction regionmotion information list and a temporary motion information list.

FIG. 28 is a view showing an example in which an encoding region mergecandidate includes address information of a block.

FIG. 29 is a view showing an example in which an encoding region mergecandidate includes address information of a block.

FIG. 30 is a view showing an example in which an encoding region mergecandidate having address information the same as that of the currentblock is set to be unavailable as a merge candidate of the currentblock.

FIG. 31 is a view showing an example in which an encoding region mergecandidate having address information the same as that of the currentblock is set to be unavailable as a merge candidate of the currentblock.

DETAILED DESCRIPTION

Hereafter, an embodiment of the present disclosure will be described indetail with reference to the accompanying drawings.

Encoding and decoding of a video is performed by the unit of block. Forexample, an encoding/decoding process such as transform, quantization,prediction, in-loop filtering, reconstruction or the like may beperformed on a coding block, a transform block, or a prediction block.

Hereinafter, a block to be encoded/decoded will be referred to as a‘current block’. For example, the current block may represent a codingblock, a transform block or a prediction block according to a currentencoding/decoding process step.

In addition, it may be understood that the term ‘unit’ used in thisspecification indicates a basic unit for performing a specificencoding/decoding process, and the term ‘block’ indicates a sample arrayof a predetermined size. Unless otherwise stated, the ‘block’ and ‘unit’may be used to have the same meaning. For example, in an embodimentdescribed below, it may be understood that a coding block and a codingunit have the same meaning.

FIG. 1 is a block diagram showing a video encoder according to anembodiment of the present disclosure.

Referring to FIG. 1, a video encoding apparatus 100 may include apicture partitioning part 110, a prediction part 120 and 125, atransform part 130, a quantization part 135, a rearrangement part 160,an entropy coding part 165, an inverse quantization part 140, an inversetransform part 145, a filter part 150, and a memory 155.

Each of the components shown in FIG. 1 is independently shown torepresent characteristic functions different from each other in a videoencoding apparatus, and it does not mean that each component is formedby the configuration unit of separate hardware or single software. Thatis, each component is included to be listed as a component forconvenience of explanation, and at least two of the components may becombined to form a single component, or one component may be dividedinto a plurality of components to perform a function. Integratedembodiments and separate embodiments of the components are also includedin the scope of the present disclosure if they do not depart from theessence of the present disclosure.

In addition, some of the components are not essential components thatperform essential functions in the present disclosure, but may beoptional components only for improving performance. The presentdisclosure can be implemented by including only components essential toimplement the essence of the present disclosure excluding componentsused for improving performance, and a structure including only theessential components excluding the optional components used forimproving performance is also included in the scope of the presentdisclosure.

The picture partitioning part 110 may partition an input picture into atleast one processing unit. At this point, the processing unit may be aprediction unit (PU), a transform unit (TU), or a coding unit (CU). Thepicture partitioning part 110 may partition a picture into a combinationof a plurality of coding units, prediction units, and transform units,and encode a picture by selecting a combination of a coding unit, aprediction unit, and a transform unit based on a predetermined criterion(e.g., a cost function).

For example, one picture may be partitioned into a plurality of codingunits. In order to partition the coding units in a picture, a recursivetree structure such as a quad tree structure may be used. A coding unitpartitioned in different coding units using a video or the largestcoding unit as a root may be partitioned to have as many child nodes asthe number of partitioned coding units. A coding unit that is notpartitioned any more according to a predetermined restriction become aleaf node. That is, when it is assumed that only square partitioning ispossible for one coding unit, the one coding unit may be partitionedinto up to four different coding units.

Hereinafter, in an embodiment of the present disclosure, the coding unitmay be used as a meaning of a unit performing encoding or a meaning of aunit performing decoding.

The prediction unit may be one that is partitioned in a shape of atleast one square, rectangle or the like of the same size within onecoding unit, or it may be any one prediction unit, among the predictionunits partitioned within one coding unit, that is partitioned to have ashape and/or size different from those of another prediction unit.

If the coding unit is not a smallest coding unit when a prediction unitthat performs intra prediction based on the coding unit is generated,intra prediction may be performed without partitioning a picture into aplurality of prediction units N×N.

The prediction part 120 and 125 may include an inter prediction part 120that performs inter prediction and an intra prediction part 125 thatperforms intra prediction. It may be determined whether to use interprediction or to perform intra prediction for a prediction unit, anddetermine specific information (e.g., intra prediction mode, motionvector, reference picture, etc.) according to each prediction method. Atthis point, a processing unit for performing prediction may be differentfrom a processing unit for determining a prediction method and specificcontent. For example, a prediction method and a prediction mode may bedetermined in a prediction unit, and prediction may be performed in atransform unit. A residual coefficient (residual block) between thegenerated prediction block and the original block may be input into thetransform part 130. In addition, prediction mode information, motionvector information and the like used for prediction may be encoded bythe entropy coding part 165 together with the residual coefficient andtransferred to a decoder. When a specific encoding mode is used, anoriginal block may be encoded as it is and transmitted to a decoderwithout generating a prediction block through the prediction part 120and 125. Here, the inter prediction part 120 and the intra predictionpart 125 may be implemented as hardware circuits. Alternatively, theinter prediction part 120 and the intra prediction part 125 may beimplemented as software instructions stored in a memory and executed bya processor.

The inter prediction part 120 may predict a prediction unit based oninformation on at least one picture among pictures before or after thecurrent picture, and in some cases, it may predict a prediction unitbased on information on a partial area that has been encoded in thecurrent picture. The inter prediction part 120 may include a referencepicture interpolation part, a motion prediction part, and a motioncompensation part.

The reference picture interpolation part may receive reference pictureinformation from the memory 155 and generate sample information of aninteger number of samples or less from the reference picture. In thecase of a luminance sample, a DCT-based 8-tap interpolation filter witha varying filter coefficient may be used to generate sample informationof an integer number of samples or less by the unit of ¼ samples. In thecase of a color difference signal, a DCT-based 4-tap interpolationfilter with a varying filter coefficient may be used to generate sampleinformation of an integer number of samples or less by the unit of ⅛samples.

The motion prediction part may perform motion prediction based on thereference picture interpolated by the reference picture interpolationpart. Various methods such as a full search-based block matchingalgorithm (FBMA), a three-step search (TSS), and a new three-step searchalgorithm (NTS) may be used as a method of calculating a motion vector.The motion vector may have a motion vector value of a unit of ½ or ¼samples based on interpolated samples. The motion prediction part maypredict a current prediction unit by varying the motion predictionmethod. Various methods such as a skip method, a merge method, anadvanced motion vector prediction (AMVP) method, an intra-block copymethod and the like may be used as the motion prediction method.

The intra prediction part 125 may generate a prediction unit based onthe information on reference samples around the current block, which issample information in the current picture. When a block in theneighborhood of the current prediction unit is a block on which interprediction has been performed and thus the reference sample is a sampleon which inter prediction has been performed, the reference sampleincluded in the block on which inter prediction has been performed maybe used in place of reference sample information of a block in theneighborhood on which intra prediction has been performed. That is, whena reference sample is unavailable, at least one reference sample amongavailable reference samples may be used in place of unavailablereference sample information.

In the intra prediction, the prediction mode may have an angularprediction mode that uses reference sample information according to aprediction direction, and a non-angular prediction mode that does notuse directional information when performing prediction. A mode forpredicting luminance information may be different from a mode forpredicting color difference information, and intra prediction modeinformation used to predict luminance information or predicted luminancesignal information may be used to predict the color differenceinformation.

If the size of the prediction unit is the same as the size of thetransform unit when intra prediction is performed, the intra predictionmay be performed for the prediction unit based on a sample on the leftside, a sample on the top-left side, and a sample on the top of theprediction unit. However, if the size of the prediction unit isdifferent from the size of the transform unit when the intra predictionis performed, the intra prediction may be performed using a referencesample based on the transform unit. In addition, intra prediction usingN×N partitioning may be used only for the smallest coding unit.

The intra prediction method may generate a prediction block afterapplying an Adaptive Intra Smoothing (AIS) filter to the referencesample according to a prediction mode. The type of the AIS filterapplied to the reference sample may vary. In order to perform the intraprediction method, the intra prediction mode of the current predictionunit may be predicted from the intra prediction mode of the predictionunit existing in the neighborhood of the current prediction unit. When aprediction mode of the current prediction unit is predicted using themode information predicted from the neighboring prediction unit, if theintra prediction modes of the current prediction unit is the same as theprediction unit in the neighborhood, information indicating that theprediction modes of the current prediction unit is the same as theprediction unit in the neighborhood may be transmitted usingpredetermined flag information, and if the prediction modes of thecurrent prediction unit and the prediction unit in the neighborhood aredifferent from each other, prediction mode information of the currentblock may be encoded by performing entropy coding.

In addition, a residual block including a prediction unit that hasperformed prediction based on the prediction unit generated by theprediction part 120 and 125 and residual coefficient information, whichis a difference value of the prediction unit with the original block,may be generated. The generated residual block may be input into thetransform part 130.

The transform part 130 may transform the residual block including theoriginal block and the residual coefficient information of theprediction unit generated through the prediction part 120 and 125 usinga transform method such as Discrete Cosine Transform (DCT) or DiscreteSine Transform (DST). Here, the DCT transform core includes at least oneamong DCT2 and DCT8, and the DST transform core includes DST7. Whetherto apply DCT or DST to transform the residual block may be determinedbased on intra prediction mode information of a prediction unit used togenerate the residual block. The transform on the residual block may beskipped. A flag indicating whether to skip the transform on the residualblock may be encoded. The transform skip may be allowed for a residualblock having a size smaller than or equal to a threshold, a lumacomponent, or a chroma component under the 4:4:4 format.

The quantization part 135 may quantize values transformed into thefrequency domain by the transform part 130. Quantization coefficientsmay vary according to the block or the importance of a video. A valuecalculated by the quantization part 135 may be provided to the inversequantization part 140 and the rearrangement part 160.

The rearrangement part 160 may rearrange coefficient values for thequantized residual coefficients.

The rearrangement part 160 may change coefficients of a two-dimensionalblock shape into a one-dimensional vector shape through a coefficientscanning method. For example, the rearrangement part 160 may scan DCcoefficients up to high-frequency domain coefficients using a zig-zagscan method, and change the coefficients into a one-dimensional vectorshape. According to the size of the transform unit and the intraprediction mode, a vertical scan of scanning the coefficients of atwo-dimensional block shape in the column direction and a horizontalscan of scanning the coefficients of a two-dimensional block shape inthe row direction may be used instead of the zig-zag scan. That is,according to the size of the transform unit and the intra predictionmode, a scan method that will be used may be determined among thezig-zag scan, the vertical direction scan, and the horizontal directionscan.

The entropy coding part 165 may perform entropy coding based on valuescalculated by the rearrangement part 160. Entropy coding may use variousencoding methods such as Exponential Golomb, Context-Adaptive VariableLength Coding (CAVLC), Context-Adaptive Binary Arithmetic Coding(CABAC), and the like.

The entropy coding part 165 may encode various information such asresidual coefficient information and block type information of a codingunit, prediction mode information, partitioning unit information,prediction unit information and transmission unit information, motionvector information, reference frame information, block interpolationinformation, and filtering information input from the rearrangement part160 and the prediction pars 120 and 125.

The entropy coding part 165 may entropy-encode the coefficient value ofa coding unit input from the rearrangement part 160.

The inverse quantization part 140 and the inverse transform part 145inverse-quantize the values quantized by the quantization part 135 andinverse-transform the values transformed by the transform part 130. Theresidual coefficient generated by the inverse quantization part 140 andthe inverse transform part 145 may be combined with the prediction unitpredicted through a motion estimation part, a motion compensation part,and an intra prediction part included in the prediction part 120 and 125to generate a reconstructed block.

The filter part 150 may include at least one among a deblocking filter,an offset correction unit, and an adaptive loop filter (ALF).

The deblocking filter may remove block distortion generated by theboundary between blocks in the reconstructed picture. In order todetermine whether to perform deblocking, whether to apply the deblockingfilter to the current block may be determined based on the samplesincluded in several columns or rows included in the block. A strongfilter or a weak filter may be applied according to the deblockingfiltering strength needed when the deblocking filter is applied to ablock. In addition, when vertical direction filtering and horizontaldirection filtering are performed in applying the deblocking filter,horizontal direction filtering and vertical direction filtering may beprocessed in parallel.

The offset correction unit may correct an offset to the original videoby the unit of sample for a video on which the deblocking has beenperformed. In order to perform offset correction for a specific picture,it is possible to use a method of dividing samples included in the videointo a certain number of areas, determining an area to perform offset,and applying the offset to the area, or a method of applying an offsetin consideration of edge information of each sample.

Adaptive Loop Filtering (ALF) may be performed based on a value obtainedby comparing the reconstructed and filtered video and the originalvideo. After dividing the samples included in the video intopredetermined groups, one filter to be applied to a corresponding groupmay be determined, and filtering may be performed differently for eachgroup. A luminance signal, which is the information related to whetherto apply ALF, may be transmitted for each coding unit (CU), and theshape and filter coefficient of an ALF filter to be applied may varyaccording to each block. In addition, an ALF filter of the same type(fixed type) may be applied regardless of the characteristic of a blockto be applied.

The memory 155 may store the reconstructed block or picture calculatedthrough the filter part 150, and the reconstructed and stored block orpicture may be provided to the prediction part 120 and 125 when interprediction is performed.

FIG. 2 is a block diagram showing a video decoder according to anembodiment of the present disclosure.

Referring to FIG. 2, a video decoder 200 may include an entropy decodingpart 210, a rearrangement part 215, an inverse quantization part 220, aninverse transform part 225, a prediction part 230 and 235, a filter part240, and a memory 245.

When a video bitstream is input from a video encoder, the inputbitstream may be decoded in a procedure opposite to that of the videoencoder.

The entropy decoding part 210 may perform entropy decoding in aprocedure opposite to that of performing entropy coding in the entropydecoding part of the video encoder. For example, various methodscorresponding to the method performed by the video encoder, such asExponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), andContext-Adaptive Binary Arithmetic Coding (CABAC), may be applied.

The entropy decoding part 210 may decode information related to intraprediction and inter prediction performed by the encoder.

The rearrangement part 215 may perform rearrangement on the bitstreamentropy-decoded by the entropy decoding part 210 based on therearrangement method performed by the encoder. The coefficientsexpressed in a one-dimensional vector shape may be reconstructed andrearranged as coefficients of two-dimensional block shape. Therearrangement part 215 may receive information related to coefficientscanning performed by the encoding part and perform reconstructionthrough a method of inverse-scanning based on the scanning orderperformed by the corresponding encoding part.

The inverse quantization part 220 may perform inverse quantization basedon a quantization parameter provided by the encoder and a coefficientvalue of the rearranged block.

The inverse transform part 225 may perform inverse transform on thetransform, i.e., DCT or DST, performed by the transform part on a resultof the quantization performed by the video encoder, i.e., inverse DCT orinverse DST. Here, the DCT transform core may include at least one amongDCT2 and DCT8, and the DST transform core may include DST7.Alternatively, when the transform is skipped in the video encoder, eventhe inverse transform part 225 may not perform the inverse transform.The inverse transform may be performed based on a transmission unitdetermined by the video encoder. The inverse transform part 225 of thevideo decoder may selectively perform a transform technique (e.g., DCTor DST) according to a plurality of pieces of information such as aprediction method, a size of a current block, a prediction direction andthe like.

The prediction part 230 and 235 may generate a prediction block based oninformation related to generation of a prediction block provided by theentropy decoder 210 and information on a previously decoded block orpicture provided by the memory 245.

As described above, if the size of the prediction unit and the size ofthe transform unit are the same when intra prediction is performed inthe same manner as the operation of the video encoder, intra predictionis performed on the prediction unit based on the sample existing on theleft side, the sample on the top-left side, and the sample on the top ofthe prediction unit. However, if the size of the prediction unit and thesize of the transform unit are different when intra prediction isperformed, intra prediction may be performed using a reference samplebased on a transform unit. In addition, intra prediction using N×Npartitioning may be used only for the smallest coding unit.

The prediction part 230 and 235 may include a prediction unitdetermination part, an inter prediction part, and an intra predictionpart. The prediction unit determination part may receive variousinformation such as prediction unit information input from the entropydecoding part 210, prediction mode information of the intra predictionmethod, information related to motion prediction of an inter predictionmethod, and the like, identify the prediction unit from the currentcoding unit, and determine whether the prediction unit performs interprediction or intra prediction. The inter prediction part 230 mayperform inter prediction on the current prediction unit based oninformation included in at least one picture among pictures before orafter the current picture including the current prediction unit by usinginformation necessary for inter prediction of the current predictionunit provided by the video encoder. Alternatively, the inter predictionpart 230 may perform inter prediction based on information on a partialarea previously reconstructed in the current picture including thecurrent prediction unit.

In order to perform inter prediction, it may be determined, based on thecoding unit, whether the motion prediction method of the prediction unitincluded in a corresponding coding unit is a skip mode, a merge mode, amotion vector prediction mode (AMVP mode), or an intra-block copy mode.

The intra prediction part 235 may generate a prediction block based onthe information on the sample in the current picture. When theprediction unit is a prediction unit that has performed intraprediction, the intra prediction may be performed based on intraprediction mode information of the prediction unit provided by the videoencoder. The intra prediction part 235 may include an Adaptive IntraSmoothing (AIS) filter, a reference sample interpolation part, and a DCfilter. The AIS filter is a part that performs filtering on thereference sample of the current block, and may determine whether toapply the filter according to the prediction mode of the currentprediction unit and apply the filter. AIS filtering may be performed onthe reference sample of the current block by using the prediction modeand AIS filter information of the prediction unit provided by the videoencoder. When the prediction mode of the current block is a mode thatdoes not perform AIS filtering, the AIS filter may not be applied.

When the prediction mode of the prediction unit is a prediction unitthat performs intra prediction based on a sample value obtained byinterpolating the reference sample, the reference sample interpolationpart may generate a reference sample of a sample unit having an integervalue or less by interpolating the reference sample. When the predictionmode of the current prediction unit is a prediction mode that generatesa prediction block without interpolating the reference sample, thereference sample may not be interpolated. The DC filter may generate aprediction block through filtering when the prediction mode of thecurrent block is the DC mode.

The reconstructed block or picture may be provided to the filter part240. The filter part 240 may include a deblocking filter, an offsetcorrection unit, and an ALF.

Information on whether a deblocking filter is applied to a correspondingblock or picture and information on whether a strong filter or a weakfilter is applied when a deblocking filter is applied may be provided bythe video encoder. The deblocking filter of the video decoder may beprovided with information related to the deblocking filter provided bythe video encoder, and the video decoder may perform deblockingfiltering on a corresponding block.

The offset correction unit may perform offset correction on thereconstructed video based on the offset correction type and offset valueinformation applied to the video when encoding is performed.

The ALF may be applied to a coding unit based on information on whetherto apply the ALF and information on ALF coefficients provided by theencoder. The ALF information may be provided to be included in aspecific parameter set.

The memory 245 may store the reconstructed picture or block and use itas a reference picture or a reference block and may provide thereconstructed picture to an output unit.

FIG. 3 is a view showing a basic coding tree unit according to anembodiment of the present disclosure.

A coding block of a maximum size may be defined as a coding tree block.A picture is partitioned into a plurality of coding tree units (CTUs).The coding tree unit is a coding unit having a maximum size and may bereferred to as a Large Coding Unit (LCU). FIG. 3 shows an example inwhich a picture is partitioned into a plurality of coding tree units.

The size of the coding tree unit may be defined at a picture level or asequence level. To this end, information indicating the size of thecoding tree unit may be signaled through a picture parameter set or asequence parameter set.

For example, the size of the coding tree unit for the entire picture ina sequence may be set to 128×128. Alternatively, at the picture level,any one among 128×128 and 256×256 may be determined as the size of thecoding tree unit. For example, the size of the coding tree unit may beset to 128×128 in a first picture, and the size of the coding tree unitmay be set to 256×256 in a second picture.

Coding blocks may be generated by partitioning a coding tree unit. Thecoding block indicates a basic unit for performing encoding/decoding.For example, prediction or transform may be performed for each codingblock, or a prediction encoding mode may be determined for each codingblock. Here, the prediction encoding mode indicates a method ofgenerating a prediction video. For example, the prediction encoding modemay include prediction within a screen (intra prediction), predictionbetween screens (inter prediction), current picture referencing (CPR) orintra-block copy (IBC), or combined prediction. For the coding block, aprediction block may be generated by using at least one predictionencoding mode among the intra prediction, the inter prediction, thecurrent picture referencing, and the combined prediction.

Information indicating the prediction encoding mode of the current blockmay be signaled through a bitstream. For example, the information may bea 1-bit flag indicating whether the prediction encoding mode is an intramode or an inter mode. Only when the prediction encoding mode of thecurrent block is determined as the inter mode, the current picturereferencing or the combined prediction may be used.

The current picture reference is for setting the current picture as areference picture and obtaining a prediction block of the current blockfrom an area that has already been encoded/decoded in the currentpicture. Here, the current picture means a picture including the currentblock. Information indicating whether the current picture reference isapplied to the current block may be signaled through a bitstream. Forexample, the information may be a 1-bit flag. When the flag is true, theprediction encoding mode of the current block may be determined as thecurrent picture reference, and when the flag is false, the predictionmode of the current block may be determined as inter prediction.

Alternatively, the prediction encoding mode of the current block may bedetermined based on a reference picture index. For example, when thereference picture index indicates the current picture, the predictionencoding mode of the current block may be determined as the currentpicture reference. When the reference picture index indicates a pictureother than the current picture, the prediction encoding mode of thecurrent block may be determined as inter prediction. That is, thecurrent picture reference is a prediction method using information on anarea in which encoding/decoding has been completed in the currentpicture, and inter prediction is a prediction method using informationon another picture in which the encoding/decoding has been completed.

The combined prediction represents an encoding mode in which two or moreamong the intra prediction, the inter prediction, and the currentpicture referencing are combined. For example, when the combinedprediction is applied, a first prediction block may be generated basedon one among the intra prediction, the inter prediction, and the currentpicture referencing, and a second prediction block may be generatedbased on another one. When the first prediction block and the secondprediction block are generated, a final prediction block may begenerated through an average operation or a weighted sum operation ofthe first prediction block and the second prediction block. Informationindicating whether the combined prediction is applied may be signaledthrough a bitstream. The information may be a 1-bit flag.

FIG. 4 is a view showing various partition types of a coding block.

The coding block may be partitioned into a plurality of coding blocksbased on quad tree partitioning, binary tree partitioning, or tripletree partitioning. The partitioned coding block may be partitioned againinto a plurality of coding blocks based on the quad tree partitioning,the binary tree partitioning, or the triple tree partitioning.

The quad tree partitioning refers to a partitioning technique thatpartitions a current block into four blocks. As a result of the quadtree partitioning, the current block may be partitioned into foursquare-shaped partitions (see ‘SPLIT_QT’ of FIG. 4 (a)).

The binary tree partitioning refers to a partitioning technique thatpartitions a current block into two blocks. Partitioning a current blockinto two blocks along the vertical direction (i.e., using a verticalline crossing the current block) may be referred to as verticaldirection binary tree partitioning, and partitioning a current blockinto two blocks along the horizontal direction (i.e., using a horizontalline crossing the current block) may be referred to as horizontaldirection binary tree partitioning. As a result of the binary treepartitioning, the current block may be partitioned into two non-squareshaped partitions. ‘SPLIT_BT_VER’ of FIG. 4 (b) shows a result of thevertical direction binary tree partitioning, and ‘SPLIT_BT_HOR’ of FIG.4 (c) shows a result of the horizontal direction binary treepartitioning.

The triple tree partitioning refers to a partitioning technique thatpartitions a current block into three blocks. Partitioning a currentblock into three blocks along the vertical direction (i.e., using twovertical lines crossing the current block) may be referred to asvertical direction triple tree partitioning, and partitioning a currentblock into three blocks along the horizontal direction (i.e., using twohorizontal lines crossing the current block) may be referred to ashorizontal direction triple tree partitioning. As a result of the tripletree partitioning, the current block may be partitioned into threenon-square shaped partitions. At this point, the width/height of apartition positioned at the center of the current block may be twice aslarge as the width/height of the other partitions. ‘SPLIT_TT_VER’ ofFIG. 4 (d) shows a result of the vertical direction triple treepartitioning, and ‘SPLIT_TT_HOR’ of FIG. 4 (e) shows a result of thehorizontal direction triple tree partitioning.

The number of times of partitioning a coding tree unit may be defined asa partitioning depth. The maximum partitioning depth of a coding treeunit may be determined at the sequence or picture level. Accordingly,the maximum partitioning depth of a coding tree unit may be differentfor each sequence or picture.

Alternatively, the maximum partitioning depth for each partitioningtechnique may be individually determined. For example, the maximumpartitioning depth allowed for the quad tree partitioning may bedifferent from the maximum partitioning depth allowed for the binarytree partitioning and/or the triple tree partitioning.

The encoder may signal information indicating at least one among thepartitioning type and the partitioning depth of the current blockthrough a bitstream. The decoder may determine the partitioning type andthe partitioning depth of a coding tree unit based on the informationparsed from the bitstream.

FIG. 5 is a view showing a partitioning pattern of a coding tree unit.

Partitioning a coding block using a partitioning technique such as quadtree partitioning, binary tree partitioning, and/or triple treepartitioning may be referred to as multi-tree partitioning.

Coding blocks generated by applying the multi-tree partitioning to acoding block may be referred to as lower coding blocks. When thepartitioning depth of a coding block is k, the partitioning depth of thelower coding blocks is set to k+1.

Contrarily, for coding blocks having a partitioning depth of k+1, acoding block having a partitioning depth of k may be referred to as anupper coding block.

The partitioning type of the current coding block may be determinedbased on at least one among a partitioning type of an upper coding blockand a partitioning type of a neighboring coding block. Here, theneighboring coding block is a coding block adjacent to the currentcoding block and may include at least one among a top neighboring blockand a left neighboring block of the current coding block, and aneighboring block adjacent to the top-left corner. Here, thepartitioning type may include at least one among whether a quad treepartitioning, whether a binary tree partitioning, binary treepartitioning direction, whether a triple tree partitioning, and tripletree partitioning direction.

In order to determine a partitioning type of a coding block, informationindicating whether the coding block can be partitioned may be signaledthrough a bitstream. The information is a 1-bit flag of ‘split_cu_flag’,and when the flag is true, it indicates that the coding block ispartitioned by a head (→quad) tree partitioning technique.

When split_cu_flag is true, information indicating whether the codingblock is quad-tree partitioned may be signaled through a bitstream. Theinformation is a 1-bit flag of split_qt_flag, and when the flag is true,the coding block may be partitioned into four blocks.

For example, in the example shown in FIG. 5, as a coding tree unit isquad-tree partitioned, four coding blocks having a partitioning depth of1 are generated. In addition, it is shown that quad tree partitioning isapplied again to the first and fourth coding blocks among the fourcoding blocks generated as a result of the quad tree partitioning. As aresult, four coding blocks having a partitioning depth of 2 may begenerated.

In addition, coding blocks having a partitioning depth of 3 may begenerated by applying the quad tree partitioning again to a coding blockhaving a partitioning depth of 2.

When quad tree partitioning is not applied to the coding block, whetherbinary tree partitioning or triple tree partitioning is performed on thecoding block may be determined in consideration of at least one amongthe size of the coding block, whether the coding block is positioned atthe picture boundary, the maximum partitioning depth, and thepartitioning type of a neighboring block. When it is determined toperform binary tree partitioning or triple tree partitioning on thecoding block, information indicating the partitioning direction may besignaled through a bitstream. The information may be a 1-bit flag ofmtt_split_cu_vertical_flag. Based on the flag, whether the partitioningdirection is a vertical direction or a horizontal direction may bedetermined. Additionally, information indicating whether binary treepartitioning or triple tree partitioning is applied to the coding blockmay be signaled through a bitstream. The information may be a 1-bit flagof mtt_split_cu_binary_flag. Based on the flag, whether binary treepartitioning or triple tree partitioning is applied to the coding blockmay be determined.

For example, in the example shown in FIG. 5, it is shown that verticaldirection binary tree partitioning is applied to a coding block having apartitioning depth of 1, vertical direction triple tree partitioning isapplied to the left-side coding block among the coding blocks generatedas a result of the partitioning, and vertical direction binary treepartitioning is applied to the right-side coding block.

Inter prediction is a prediction encoding mode that predicts a currentblock by using information of a previous picture. For example, a blockat the same position as the current block in the previous picture(hereinafter, a collocated block) may be set as the prediction block ofthe current block. Hereinafter, a prediction block generated based on ablock at the same position as the current block will be referred to as acollocated prediction block.

On the other hand, when an object existing in the previous picture hasmoved to another position in the current picture, the current block maybe effectively predicted by using a motion of the object. For example,when the moving direction and the size of an object can be known bycomparing the previous picture and the current picture, a predictionblock (or a prediction video) of the current block may be generated inconsideration of motion information of the object. Hereinafter, theprediction block generated using motion information may be referred toas a motion prediction block.

A residual block may be generated by subtracting the prediction blockfrom the current block. At this point, when there is a motion of anobject, the energy of the residual block may be reduced by using themotion prediction block instead of the collocated prediction block, andtherefore, compression performance of the residual block can beimproved.

As described above, generating a prediction block by using motioninformation may be referred to as motion compensation prediction. Inmost inter prediction, a prediction block may be generated based on themotion compensation prediction.

The motion information may include at least one among a motion vector, areference picture index, a prediction direction, and a bidirectionalweight index. The motion vector represents the moving direction and thesize of an object. The reference picture index specifies a referencepicture of the current block among reference pictures included in areference picture list. The prediction direction indicates any one amongunidirectional L0 prediction, unidirectional L1 prediction, andbidirectional prediction (L0 prediction and L1 prediction). According tothe prediction direction of the current block, at least one among motioninformation in the L0 direction and motion information in the L1direction may be used. The bidirectional weight index specifies aweighting value applied to a L0 prediction block and a weighting valueapplied to a L1 prediction block.

FIG. 6 is a flowchart showing an inter prediction method according to anembodiment of the present disclosure.

Referring to FIG. 6, the inter prediction method includes the steps ofdetermining an inter prediction mode of a current block (S601),acquiring motion information of the current block according to thedetermined inter prediction mode (S602), and performing motioncompensation prediction for the current block based on the acquiredmotion information (S603).

Here, the inter prediction mode represents various techniques fordetermining motion information of the current block, and may include aninter prediction mode that uses translational motion information and aninter prediction mode that uses affine motion information. For example,the inter prediction mode using translational motion information mayinclude a merge mode and a motion vector prediction mode, and the interprediction mode using affine motion information may include an affinemerge mode and an affine motion vector prediction mode. The motioninformation of the current block may be determined based on aneighboring block adjacent to the current block or information parsedfrom a bitstream according to the inter prediction mode.

Hereinafter, the inter prediction method using affine motion informationwill be described in detail.

FIG. 7 is a view showing a nonlinear motion of an object.

A nonlinear motion of an object may be generated in a video. Forexample, as shown in the example of FIG. 7, a nonlinear motion of anobject, such as zoom-in, zoom-out, rotation, affine transform or thelike of a camera, may occur. When a nonlinear motion of an objectoccurs, the motion of the object cannot be effectively expressed with atranslational motion vector. Accordingly, encoding efficiency can beimproved by using an affine motion instead of a translational motion inan area where a nonlinear motion of an object occurs.

FIG. 8 is a flowchart showing an inter prediction method based on anaffine motion according to an embodiment of the present disclosure.

Whether an inter prediction technique based on an affine motion isapplied to the current block may be determined based on the informationparsed from a bitstream. Specifically, whether the inter predictiontechnique based on an affine motion is applied to the current block maybe determined based on at least one among a flag indicating whether theaffine merge mode is applied to the current block and a flag indicatingwhether the affine motion vector prediction mode is applied to thecurrent block.

When the inter prediction technique based on an affine motion is appliedto the current block, an affine motion model of the current block may bedetermined (S801). The affine motion model may be determined as at leastone among a six-parameter affine motion model and a four-parameteraffine motion model. The six-parameter affine motion model expresses anaffine motion using six parameters, and the four-parameter affine motionmodel expresses an affine motion using four parameters.

Equation 1 expresses an affine motion using six parameters. The affinemotion represents a translational motion for a predetermined areadetermined by affine seed vectors.

$\begin{matrix}{{v_{x} = {{ax} - {by} + e}}{v_{y} = {{cx} + {dy} + f}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

When an affine motion is expressed using six parameters, a complicatedmotion can be expressed. However, as the number of bits required forencoding each of the parameters increases, encoding efficiency may belowered. Accordingly, the affine motion may be expressed using fourparameters. Equation 2 expresses an affine motion using four parameters.

$\begin{matrix}{{v_{x} = {{ax} - {by} + e}}{v_{y} = {{bx} + {ay} + f}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Information for determining an affine motion model of the current blockmay be encoded and signaled through a bitstream. For example, theinformation may be a 1-bit flag of ‘affine_type_flag’. When the value ofthe flag is 0, it may indicate that a 4-parameter affine motion model isapplied, and when the value of the flag is 1, it may indicate that a6-parameter affine motion model is applied. The flag may be encoded bythe unit of slice, tile, or block (e.g., by the unit of coding block orcoding tree). When a flag is signaled at the slice level, an affinemotion model determined at the slice level may be applied to all blocksbelonging to the slice.

Alternatively, an affine motion model of the current block may bedetermined based on an affine inter prediction mode of the currentblock. For example, when the affine merge mode is applied, the affinemotion model of the current block may be determined as a 4-parametermotion model. On the other hand, when the affine motion vectorprediction mode is applied, information for determining the affinemotion model of the current block may be encoded and signaled through abitstream. For example, when the affine motion vector prediction mode isapplied to the current block, the affine motion model of the currentblock may be determined based on the 1-bit flag of ‘affine_type_flag’.

Next, an affine seed vector of the current block may be derived (S802).When a 4-parameter affine motion model is selected, motion vectors attwo control points of the current block may be derived. On the otherhand, when a 6-parameter affine motion model is selected, motion vectorsat three control points of the current block may be derived. The motionvector at a control point may be referred to as an affine seed vector.The control point may include at least one among the top-left corner,the top-right corner, and the bottom-left corner of the current block.

FIG. 9 is a view showing an example of affine seed vectors of eachaffine motion model.

In the 4-parameter affine motion model, affine seed vectors may bederived for two among the top-left corner, the top-right corner, and thebottom-left corner. For example, as shown in the example of FIG. 9 (a),when a 4-parameter affine motion model is selected, an affine vector maybe derived using the affine seed vector sv₀ for the top-left corner ofthe current block (e.g., top-left sample (x1, y1)) and the affine seedvector sv₁ for the top-right corner of the current block (e.g., thetop-right sample (x1, y1)). It is also possible to use an affine seedvector for the bottom-left corner instead of the affine seed vector forthe top-left corner, or use an affine seed vector for the bottom-leftcorner instead of the affine seed vector for the top-right corner.

In the 6-parameter affine motion model, affine seed vectors may bederived for the top-left corner, the top-right corner, and thebottom-left corner. For example, as shown in the example of FIG. 9 (b),when a 6-parameter affine motion model is selected, an affine vector maybe derived using the affine seed vector sv₀ for the top-left corner ofthe current block (e.g., top-left sample (x1, y1)), the affine seedvector sv₁ for the top-right corner of the current block (e.g., thetop-right sample (x1, y1)), and the affine seed vector sv₂ for thetop-left corner of the current block (e.g., top-left sample (x2, y2)).

In the embodiment described below, in the 4-parameter affine motionmodel, the affine seed vectors of the top-left control point and thetop-right control point will be referred to as a first affine seedvector and a second affine seed vector, respectively. In the embodimentsusing the first affine seed vector and the second affine seed vectordescribed below, at least one among the first affine seed vector and thesecond affine seed vector may be replaced by the affine seed vector ofthe bottom-left control point (a third affine seed vector) or the affineseed vector of the bottom-right control point (a fourth affine seedvector).

In addition, in the 6-parameter affine motion model, the affine seedvectors of the top-left control point, the top-right control point, andthe bottom-left control point will be referred to as a first affine seedvector, a second affine seed vector, and a third affine seed vector,respectively. In the embodiments using the first affine seed vector, thesecond affine seed vector, and the third affine seed vector describedbelow, at least one among the first affine seed vector, the secondaffine seed vector, and the third affine seed vector may be replaced bythe affine seed vector of the bottom-right control point (a fourthaffine seed vector).

An affine vector may be derived for each subblock by using the affineseed vectors (S803). Here, the affine vector represents a translationalmotion vector derived based on the affine seed vectors. The affinevector of a subblock may be referred to as an affine subblock motionvector or a subblock motion vector.

FIG. 10 is a view showing an example of affine vectors of subblocks in a4-parameter motion model.

The affine vector of the subblock may be derived based on the positionof the control point, the position of the subblock, and the affine seedvector. For example, Equation 3 shows an example of deriving an affinesubblock vector.

$\begin{matrix}{{v_{x} = {{\frac{\left( {{sv_{1x}} - {sv_{0x}}} \right)}{\left( {x_{1} - x_{0}} \right)}\left( {x - x_{0}} \right)} - {\frac{\left( {{sv_{1y}} - {sv_{0y}}} \right)}{\left( {x_{1} - x_{0}} \right)}\left( {y - y_{0}} \right)} + {sv_{0x}}}}{v_{y} = {{\frac{\left( {{sv_{1y}} - {sv_{0y}}} \right)}{\left( {x_{1} - x_{0}} \right)}\left( {x - x_{0}} \right)} - {\frac{\left( {{sv_{1x}} - {sv_{0x}}} \right)}{\left( {x_{1} - x_{0}} \right)}\left( {y - y_{0}} \right)} + {sv_{0y}}}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In Equation 3, (x, y) denotes the position of a subblock. Here, theposition of a subblock indicates the position of a reference sampleincluded in the subblock. The reference sample may be a samplepositioned at the top-left corner of the subblock, or a sample of whichat least one among the x-axis and y-axis coordinates is a center point.(x₀, y₀) denotes the position of the first control point, and (sv_(0x),sv_(0y)) denotes the first affine seed vector. In addition, (x₁, y₁)denotes the position of the second control point, and (sv_(1x), sv_(1y))denotes the second affine seed vector.

When the first control point and the second control point correspond tothe top-left corner and the top-right corner of the current blockrespectively, x₁−x₀ may be set to a value equal to the width of thecurrent block.

Thereafter, motion compensation prediction for each subblock may beperformed using the affine vector of each subblock (S804). As a resultof performing the motion compensation prediction, a prediction block foreach subblock may be generated. The prediction blocks of the subblocksmay be set as the prediction blocks of the current block.

Next, an inter prediction method using translational motion informationwill be described in detail.

Motion information of the current block may be derived from motioninformation of the current block another block (4 another block). Here,another block may be a block encoded/decoded by inter prediction beforethe current block. Setting the motion information of the current blockto be equal to the motion information of another block may be defined asa merge mode. In addition, setting the motion vector of another block asthe prediction value of the motion vector of the current block may bedefined as a motion vector prediction mode.

FIG. 11 is a flowchart showing a process of deriving motion informationof a current block using a merge mode.

A merge candidate of the current block may be derived (S1101). The mergecandidate of the current block may be derived from a blockencoded/decoded by inter prediction before the current block.

FIG. 12 is a view showing an example of candidate blocks used forderiving a merge candidate.

The candidate blocks may include at least one among neighboring blocksincluding a sample adjacent to the current block or non-neighboringblocks including a sample not adjacent to the current block.Hereinafter, samples for determining candidate blocks are defined asreference samples. In addition, a reference sample adjacent to thecurrent block is referred to as a neighboring reference sample, and areference sample not adjacent to the current block is referred to as anon-neighboring reference sample.

The neighboring reference sample may be included in a neighboring columnof the leftmost column of the current block or a neighboring row of theuppermost row of the current block. For example, when the coordinates ofthe top-left sample of the current block is (0, 0), at least one among ablock including a reference sample at the position of (−1, H−1), a blockincluding a reference sample at the position of (W−1, −1), a blockincluding a reference sample at the position of (W, −1), a blockincluding a reference sample at the position of (−1, H), and a blockincluding a reference sample at the position of (−1, −1) may be used asa candidate block. Referring to the drawing, neighboring blocks of index0 to 4 may be used as candidate blocks.

The non-neighboring reference sample represents a sample of which atleast one among an x-axis distance and a y-axis distance from areference sample adjacent to the current block has a predefined value.For example, at least one among a block including a reference sample ofwhich the x-axis distance from the left reference sample is a predefinedvalue, a block including a non-neighboring sample of which the y-axisdistance from the top reference sample is a predefined value, and ablock including a non-neighboring sample of which the x-axis distanceand the y-axis distance from the top-left reference sample arepredefined values may be used as a candidate block. The predefinedvalues may be a natural number such as 4, 8, 12, 16 or the like.Referring to the drawing, at least one among the blocks of index 5 to 26may be used as a candidate block.

A sample not positioned on the same vertical line, horizontal line, ordiagonal line as the neighboring reference sample may be set as anon-neighboring reference sample.

FIG. 13 is a view showing positions of reference samples.

As shown in the example of FIG. 13, the x coordinates of the topnon-neighboring reference samples may be set to be different from the xcoordinates of the top neighboring reference samples. For example, whenthe position of the top neighboring reference sample is (W−1, −1), theposition of a top non-neighboring reference sample separated as much asN from the top neighboring reference sample on the y-axis may be set to((W/2)−1, −1−N), and the position of a top non-neighboring referencesample separated as much as 2N from the top neighboring reference sampleon the y-axis may be set to (0, −1−2N). That is, the position of anon-adjacent reference sample may be determined based on the position ofan adjacent reference sample and a distance from the adjacent referencesample.

Hereinafter, a candidate block including a neighboring reference sampleamong the candidate blocks is referred to as a neighboring block, and ablock including a non-neighboring reference sample is referred to as anon-neighboring block.

When the distance between the current block and the candidate block isgreater than or equal to a threshold value, the candidate block may beset to be unavailable as a merge candidate. The threshold value may bedetermined based on the size of the coding tree unit. For example, thethreshold value may be set to the height (ctu_height) of the coding treeunit or a value obtained by adding or subtracting an offset to or fromthe height (e.g., ctu_height±N) of the coding tree unit. The offset N isa value predefined in the encoder and the decoder, and may be set to 4,8, 16, 32 or ctu_height.

When the difference between the y-axis coordinate of the current blockand the y-axis coordinate of a sample included in a candidate block isgreater than the threshold value, the candidate block may be determinedto be unavailable as a merge candidate.

Alternatively, a candidate block that does not belong to the same codingtree unit as the current block may be set to be unavailable as a mergecandidate. For example, when a reference sample deviates from the topboundary of a coding tree unit to which the current block belongs, acandidate block including the reference sample may be set to beunavailable as a merge candidate.

When the top boundary of the current block is adjacent to the topboundary of the coding tree unit, a plurality of candidate blocks isdetermined to be unavailable as a merge candidate, and thus theencoding/decoding efficiency of the current block may decrease. To solvethis problem, candidate blocks may be set so that the number ofcandidate blocks positioned on the left side of the current block isgreater than the number of candidate blocks positioned on the top of thecurrent block.

FIG. 14 is a view showing an example of candidate blocks used forderiving a merge candidate.

As shown in the example of FIG. 14, top blocks belonging to top N blockcolumns of the current block and left-side blocks belonging to Mleft-side block columns of the current block may be set as candidateblocks. At this point, the number of left-side candidate blocks may beset to be greater than the number of top candidate blocks by setting Mto be greater than N.

For example, the difference between the y-axis coordinate of thereference sample in the current block and the y-axis coordinate of thetop block that can be used as a candidate block may be set not to exceedN times of the height of the current block. In addition, the differencebetween the x-axis coordinate of the reference sample in the currentblock and the x-axis coordinate of the left-side block that can be usedas a candidate block may be set not to exceed M times of the width ofthe current block.

For example, in the example shown in FIG. 14, it is shown that blocksbelonging to the top two block columns of the current block and blocksbelonging to the left five block columns of the current block are set ascandidate blocks.

As another example, when a candidate block does not belong to a codingtree unit the same as that of the current block, a merge candidate maybe derived using a block belonging to the same coding tree unit as thecurrent block or a block including a reference sample adjacent to theboundary of the coding tree unit, instead of the candidate block.

FIG. 15 is a view showing an example in which the position of areference sample is changed.

When a reference sample is included in a coding tree unit different fromthe current block, and the reference sample is not adjacent to theboundary of the coding tree unit, a candidate block may be determinedusing a reference sample adjacent to the boundary of the coding treeunit, instead of the reference sample.

For example, in the examples shown in FIGS. 15 (a) and 15 (b), when thetop boundary of the current block and the top boundary of the codingtree unit are in contact with each other, the reference samples on thetop of the current block belong to a coding tree unit different from thecurrent block. Among the reference samples belonging to the coding treeunit different from the current block, a reference sample not adjacentto the top boundary of the coding tree unit may be replaced with asample adjacent to the top boundary of the coding tree unit.

For example, as shown in the example of FIG. 15 (a), the referencesample at position 6 is replaced with the sample at position 6′positioned at the top boundary of the coding tree unit, and as shown inthe example of FIG. 15 (b), the reference sample at position 15 isreplaced with the sample at position 15′ positioned at the top boundaryof the coding tree unit. At this point, the y coordinate of thereplacement sample is changed to a position adjacent to the coding treeunit, and the x coordinate of the replacement sample may be set to beequal to the reference sample. For example, the sample at position 6′may have the same x-coordinate as the sample at position 6, and thesample at position 15′ may have the same x-coordinate as the sample atposition 15.

Alternatively, a value obtained by adding or subtracting an offset to orfrom the x coordinate of the reference sample may be set as the xcoordinate of the replacement sample. For example, when thex-coordinates of the neighboring reference sample positioned on the topof the current block and the non-neighboring reference sample are thesame, a value obtained by adding or subtracting an offset to or from thex coordinate of the reference sample may be set as the x coordinate ofthe replacement sample. This is for preventing the replacement samplereplacing the non-neighboring reference sample from being placed at thesame position as another non-neighboring reference sample or neighboringreference sample.

FIG. 16 is a view showing an example in which the position of areference sample is changed.

In replacing a reference sample that is included in a coding tree unitdifferent from the current block and is not adjacent to the boundary ofthe coding tree unit with a sample positioned at the boundary of thecoding tree unit, a value obtained by adding or subtracting an offset toand from the x coordinate of the reference sample may be set as thex-coordinate of the replacement sample.

For example, in the example shown in FIG. 16, the reference sample atposition 6 and the reference sample at position 15 may be replaced withthe sample at position 6′ and the sample at position 15′ respectively,of which the y coordinates are the same as that of the row adjacent tothe top boundary of the coding tree unit. At this point, thex-coordinate of the sample at position 6′ may be set to a value obtainedby subtracting W/2 from the x-coordinate of the reference sample atposition 6, and the x-coordinate of the sample at position 15′ may beset to a value obtained by subtracting W−1 from the x-coordinate of thereference sample at position 15.

Unlike the examples shown in FIGS. 15 and 16, the y coordinate of therow positioned on the top of the uppermost row of the current block orthe y coordinate of the top boundary of the coding tree unit may be setas the y coordinate of the replacement sample.

Although not shown, a sample replacing the reference sample may bedetermined based on the left-side boundary of the coding tree unit. Forexample, when the reference sample is not included in the same codingtree unit as the current block and is not adjacent to the left-sideboundary of the coding tree unit, the reference sample may be replacedwith a sample adjacent to the left-side boundary of the coding treeunit. At this point, the replacement sample may have a y-coordinate thesame as that of the reference sample, or may have a y-coordinateobtained by adding or subtracting an offset to and from the y-coordinateof the reference sample.

Thereafter, a block including the replacement sample may be set as acandidate block, and a merge candidate of the current block may bederived based on the candidate block.

A merge candidate may also be derived from a temporally neighboringblock included in a picture different from the current block. Forexample, a merge candidate may be derived from a collocated blockincluded in a collocated picture.

The motion information of the merge candidate may be set to be equal tothe motion information of the candidate block. For example, at least oneamong a motion vector, a reference picture index, a predictiondirection, and a bidirectional weight index of the candidate block maybe set as motion information of the merge candidate.

A merge candidate list including merge candidates may be generated(S1102). The merge candidates may be divided into an adjacent mergecandidate derived from a neighboring block adjacent to the current blockand a non-adjacent merge candidate derived from a non-neighboring block.

Indexes of the merge candidates in the merge candidate list may beassigned in a predetermined order. For example, an index assigned to anadjacent merge candidate may have a value smaller than an index assignedto a non-adjacent merge candidate. Alternatively, an index may beassigned to each of the merge candidates based on the index of eachblock shown in FIG. 12 or 14.

When a plurality of merge candidates is included in the merge candidatelist, at least one among the plurality of merge candidates may beselected (S1103). At this point, information indicating whether motioninformation of the current block is derived from an adjacent mergecandidate may be signaled through a bitstream. The information may be a1-bit flag. For example, a syntax element isAdjancentMergeFlagindicating whether the motion information of the current block isderived from an adjacent merge candidate may be signaled through abitstream. When the value of the syntax element isAdjancentMergeFlag is1, motion information of the current block may be derived based on theadjacent merge candidate. On the other hand, when the value of thesyntax element isAdjancentMergeFlag is 0, motion information of thecurrent block may be derived based on a non-adjacent merge candidate.

Table 1 shows a syntax table including syntax elementisAdjancentMergeFlag.

TABLE 1 coding_unit (x0, y0, cbWidth, cbHeight, treeType) { Descriptor if (slice_type ! = I) {    pred_mode_flag ae(v)  }  if(CuPredMode[x0][y0] = = MODE_INTRA) {   if (treeType = = SINGLE_TREE ∥treeType = = DUAL_TREE_LUMA) {    intra_luma_mpm_flag[x0][y0]    if(intra_luma_mpm_flag[x0][y0])     intra_luma_mpm_id[x0][y0] ae(v)   else     intra_luma_mpm_remainder[x0][y0] ae(v)   }   if (treeType == SINGLE_TREE ∥ treeType = = DUAL_TREE_CHROMA)   intra_chroma_pred_mode[x0][y0] ae(v)  } else {   if(cu_skip_falg[x0][y0]) {    if (MaxNumMergeCand > 1) {   isAdjacentMergeflag ae(v)    if (isAdjcanetMergeflag){   merge_idx[x0][y0] ae(v)    } else {     NA_merge_idx[x0][y0] ae(v)   }   }  } else {/* MODE_INTER*/  merge_flag[x0][y0] ae(v)   if(merge_flag[x0][y0]){    if (MaxNumMergeCand > 1){   isAdjacentMergeflag ae(v)    if (isAdjcanetMergeflag){    merge_idx[x0][y0] ae(v)    } else {     NA_merge_idx[x0][y0] ae(v)   }   }  }  if (CuPredMode[x0][y0] ! = MODE_INTRA)   cu_cbf ae(v)  if(cu_cbf) {   transform_tree (x0, y0, cbWidth, cbHeight, treeType) }

Information for specifying any one among a plurality of merge candidatesmay be signaled through a bitstream. For example, information indicatingan index of any one among the merge candidates included in the mergecandidate list may be signaled through a bitstream.

When isAdjacentMergeflag is 1, syntax element merge_idx specifying anyone among the adjacent merge candidates may be signaled. The maximumvalue of syntax element merge_idx may be set to a value obtained bysubtracting 1 from the number of adjacent merge candidates.

When isAdjacentMergeflag is 0, syntax element NA_merge_idx specifyingany one among the non-adjacent merge candidates may be signaled. Thesyntax element NA_merge_idx represents a value obtained by subtractingthe number of adjacent merge candidates from the index of thenon-adjacent merge candidate. The decoder may select a non-adjacentmerge candidate by adding the number of adjacent merge candidates to anindex specified by NA_merge_idx.

When the number of merge candidates included in the merge candidate listis smaller than a threshold value, the merge candidate included in theprediction region motion information list may be added to the mergecandidate list. Here, the threshold value may be the maximum number ofmerge candidates that can be included in the merge candidate list or avalue obtained by subtracting an offset from the maximum number of mergecandidates. The offset may be a natural number such as 1, 2, or thelike. The inter region motion information list may include a mergecandidate derived based on a block encoded/decoded before the currentblock.

The prediction region motion information list includes a merge candidatederived from a block encoded/decoded based on inter prediction in thecurrent picture. For example, motion information of a merge candidateincluded in the prediction region motion information list may be set tobe equal to motion information of a block encoded/decoded based on interprediction. Here, the motion information may include at least one amonga motion vector, a reference picture index, a prediction direction, anda bidirectional weight index.

For convenience of explanation, a merge candidate included in theprediction region motion information list will be referred to as aprediction region merge candidate.

The maximum number of merge candidates that can be included in theprediction region motion information list may be predefined by anencoder and a decoder. For example, the maximum number of mergecandidates that can be included in the prediction region motioninformation list may be 1, 2, 3, 4, 5, 6, 7, 8 or more (e.g., 16).

Alternatively, information indicating the maximum number of mergecandidates that can be included in the prediction region motioninformation list may be signaled through a bitstream. The informationmay be signaled at a sequence, picture, or slice level. The informationmay indicate the maximum number of merge candidates that can be includedin the prediction region motion information list. Alternatively, theinformation may indicate a difference between the maximum number ofmerge candidates that can be included in the prediction region motioninformation list and the maximum number of merge candidates that can beincluded in the merge candidate list.

Alternatively, the maximum number of merge candidates of the predictionregion motion information list may be determined according to the sizeof a picture, the size of a slice, or the size of a coding tree unit.

The prediction region motion information list may be initialized by theunit of picture, slice, tile, brick, coding tree unit, or coding treeunit line (row or column). For example, when a slice is initialized, theprediction region motion information list is also initialized, and theprediction region motion information list may not include any mergecandidate.

Alternatively, information indicating whether to initialize theprediction region motion information list may be signaled through abitstream. The information may be signaled at the slice, tile, brick, orblock level. Until the information indicates to initialize theprediction region motion information list, a previously configuredprediction region motion information list may be used.

Alternatively, information on the initial prediction region mergecandidate may be signaled through a picture parameter set or a sliceheader. Although the slice is initialized, the prediction region motioninformation list may include the initial prediction region mergecandidate. Accordingly, a prediction region merge candidate may be usedfor a block that is the first encoding/decoding target in the slice.

Alternatively, a prediction region merge candidate included in theprediction region motion information list of a previous coding tree unitmay be set as the initial prediction region merge candidate. Forexample, among the prediction region merge candidates included in theprediction region motion information list of a previous coding treeunit, a prediction region merge candidate having the smallest index or aprediction region merge candidate having the largest index may be set asthe initial prediction region merge candidate.

Blocks are encoded/decoded according to an encoding/decoding order, andblocks encoded/decoded based on inter prediction may be sequentially setas a prediction region merge candidate according to an encoding/decodingorder.

FIG. 17 is a flowchart showing a process of updating a prediction regionmotion information list.

When inter prediction is performed on the current block (S1701), aprediction region merge candidate may be derived based on the currentblock (S1702). Motion information of the prediction region mergecandidate may be set to be equal to the motion information of thecurrent block.

When the prediction region motion information list is empty (S1703), theprediction region merge candidate derived based on the current block maybe added to the prediction region motion information list (S1704).

When the prediction region motion information list already includes theprediction region merge candidate (S1703), a redundancy check may beperformed on the motion information of the current block (or theprediction region merge candidate derived based on the current block)(S1705). The redundancy check is for determining whether motioninformation of a prediction region merge candidate previously stored inthe prediction region motion information list and motion information ofthe current block are the same. The redundancy check may be performed onall prediction region merge candidates previously stored in theprediction region motion information list. Alternatively, the redundancycheck may be performed on prediction region merge candidates having anindex larger than a threshold value or smaller than a threshold valueamong the prediction region merge candidates previously stored in theprediction region motion information list.

When an inter prediction merge candidate having the same motioninformation as the motion information of the current block is notincluded, the prediction region merge candidate derived based on thecurrent block may be added to the prediction region motion informationlist (S1708). Whether the inter prediction merge candidates are the samemay be determined based on whether motion information (e.g., a motionvector and/or a reference picture index) of the inter prediction mergecandidates is the same.

At this point, when the maximum number of prediction region mergecandidates are already stored in the prediction region motioninformation list (S1706), the oldest prediction region merge candidateis deleted (S1707), and the prediction region merge candidate derivedbased on the current block may be added to the prediction region motioninformation list (S1708). Here, the oldest prediction region mergecandidate may be a prediction region merge candidate having the largestindex or a prediction region merge candidate having the smallest index.

Each of the prediction region merge candidates may be identified by anindex. When a prediction region merge candidate derived from the currentblock is added to the prediction region motion information list, thelowest index (e.g., 0) is assigned to the prediction region mergecandidate, and indexes of the previously stored prediction region mergecandidates may be increased by 1. At this point, when the maximum numberof inter prediction merge candidates are already stored in theprediction region motion information list, a prediction region mergecandidate having the largest index is removed.

Alternatively, when the prediction region merge candidate derived fromthe current block is added to the prediction region motion informationlist, the largest index may be assigned to the prediction region mergecandidate. For example, when the number of inter prediction mergecandidates previously stored in the prediction region motion informationlist is smaller than a maximum value, an index having the same value asthe number of previously stored inter prediction merge candidates may beassigned to the prediction region merge candidate. Alternatively, whenthe number of inter prediction merge candidates previously stored in theprediction region motion information list is the same as the maximumvalue, an index subtracting 1 from the maximum value may be assigned tothe prediction region merge candidate. In addition, a prediction regionmerge candidate having the smallest index is removed, and indexes ofremaining previously stored prediction region merge candidates may bedecreased by 1.

FIG. 18 is a view showing an embodiment of updating a prediction regionmerge candidate list.

It is assumed that as the prediction region merge candidate derived fromthe current block is added to the prediction region merge candidatelist, the largest index is assigned to the prediction region mergecandidate. In addition, it is assumed that the maximum number ofprediction region merge candidates is already stored in the predictionregion merge candidate list.

When the prediction region merge candidate HmvpCand[n+1] derived fromthe current block is added to the prediction region merge candidate listHmvpCandList, the prediction region merge candidate HmvpCand[0] havingthe smallest index among the previously stored prediction region mergecandidates are deleted, and the indexes of the remaining predictionregion merge candidates may be decreased by 1. In addition, the index ofthe prediction region merge candidate HmvpCand[n+1] derived from thecurrent block may be set to a maximum value (n in the example shown inFIG. 18).

When a prediction region merge candidate the same as the predictionregion merge candidate derived based on the current block is previouslystored (S1705), the prediction region merge candidate derived based onthe current block may not be added to the prediction region motioninformation list (S1709).

Alternatively, as the prediction region merge candidate derived based onthe current block is added to the prediction region motion informationlist, a previously stored prediction region merge candidate that is thesame as the prediction region merge candidate may be removed. In thiscase, an effect the same as newly updating the index of the previouslystored prediction region merge candidate is obtained.

FIG. 19 is a view showing an example in which an index of a previouslystored prediction region merge candidate is updated.

When the index of a previously stored inter prediction merge candidatemvCand that is the same as the prediction region merge candidate mvCandderived based on the current block is hIdx, the previously stored interprediction merge candidate is deleted, and indexes of inter predictionmerge candidates having an index larger than hIdx may be decreased by 1.For example, in the example shown in FIG. 19, it is shown thatHmvpCand[2] the same as mvCand is deleted from the prediction regionmotion information list HvmpCandList, and the indexes of HmvpCand[3] toHmvpCand[n] are decreased by 1.

In addition, the prediction region merge candidate mvCand derived basedon the current block may be added to the end of the prediction regionmotion information list.

Alternatively, the index assigned to the previously stored predictionregion merge candidate that is the same as the prediction region mergecandidate derived based on the current block may be updated. Forexample, the index of the previously stored prediction region mergecandidate may be changed to a minimum value or a maximum value.

It may be set not to add motion information of blocks included in apredetermined region to the prediction region motion information list.For example, a prediction region merge candidate derived based on motioninformation of a block included in the merge processing area may not beadded to the prediction region motion information list. Since anencoding/decoding order is not defined for the blocks included in themerge processing area, it is inappropriate to use motion information ofany one among the blocks for inter prediction of another block.Accordingly, prediction region merge candidates derived based on theblocks included in the merge processing area may not be added to theprediction region motion information list.

Alternatively, it may be set not to add motion information of a blocksmaller than a preset size to the prediction region motion informationlist. For example, a prediction region merge candidate derived based onmotion information of a coding block having a width or a height smallerthan 4 or 8 or motion information of a coding block having a 4×4 sizemay not be added to the prediction region motion information list.

When motion compensation prediction is performed by the unit ofsubblock, a prediction region merge candidate may be derived based onmotion information of a representative subblock among a plurality ofsubblocks included in the current block. For example, when a subblockmerge candidate is used for the current block, a prediction region mergecandidate may be derived based on motion information of a representativesubblock among the subblocks.

Motion vectors of the subblocks may be derived in the following order.First, any one among the merge candidates included in the mergecandidate list of the current block is selected, and an initial shiftvector (shVector) may be derived based on the motion vector of theselected merge candidate. Then, a shift subblock, in which the positionof the reference sample is (xColSb, yColSb), may be derived as theinitial shift vector is added at the position (xSb, ySb) of thereference sample (e.g., the top-left sample or the sample at the center)of each subblock in the coding block. Equation 4 shows an equation forderiving a shift subblock.

$\begin{matrix}{\left( {{xColSb},{yColSb}} \right) = \left( {{{{xSb} + {{shVecto}{r\lbrack 0\rbrack}}} ⪢ 4},{{{ySb} + {{shVector}\lbrack 1\rbrack}} ⪢ 4}} \right)} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Then, the motion vector of a collocated block corresponding to thecenter position of the subblock including (xColSb, yColSb) may be set asthe motion vector of the subblock including (xSb, ySb).

The representative subblock may mean a subblock including the top-leftsample or the sample at the center of the current block.

FIG. 20 is a view showing the position of a representative subblock.

FIG. 20 (a) shows an example in which the subblock positioned at thetop-left of the current block is set as the representative subblock, andFIG. 20(b) shows an example in which the subblock positioned at thecenter of the current block is set as the representative subblock. Whenmotion compensation prediction is performed by unit of subblock, aprediction region merge candidate of the current block may be derivedbased on the motion vector of the subblock including the top-left sampleof the current block or the subblock including the sample at the centerof the current block.

It may be determined whether to use the current block as a predictionregion merge candidate, based on the inter prediction mode of thecurrent block. For example, a block encoded/decoded based on an affinemotion model may be set to be unavailable as a prediction region mergecandidate. Accordingly, although the current block is encoded/decoded byinter prediction, when the inter prediction mode of the current block isthe affine prediction mode, the inter prediction motion information listmay not be updated based on the current block.

Alternatively, the prediction region merge candidate may be derivedbased on at least one subblock vector among the subblocks included inthe block encoded/decoded based on the affine motion model. For example,the prediction region merge candidate may be derived using a subblockpositioned at the top-left, a subblock positioned at the center, or asubblock positioned at the top-right side of the current block.Alternatively, an average value of subblock vectors of a plurality ofsubblocks may be set as the motion vector of the prediction region mergecandidate.

Alternatively, the prediction region merge candidate may be derivedbased on an average value of affine seed vectors of the blockencoded/decoded based on the affine motion model. For example, anaverage of at least one among the first affine seed vector, the secondaffine seed vector, and the third affine seed vector of the currentblock may be set as the motion vector of the prediction region mergecandidate.

Alternatively, a prediction region motion information list may beconfigured for each inter prediction mode. For example, at least oneamong a prediction region motion information list for a blockencoded/decoded by intra-block copy, a prediction region motioninformation list for a block encoded/decoded based on a translationalmotion model, and a prediction region motion information list for ablock encoded/decoded based on an affine motion model may be defined.According to the inter prediction mode of the current block, any oneamong a plurality of prediction region motion information lists may beselected.

FIG. 21 is a view showing an example in which a prediction region motioninformation list is generated for each inter prediction mode.

When a block is encoded/decoded based on a non-affine motion model, aprediction region merge candidate mvCand derived based on the block maybe added to a prediction region non-affine motion information listHmvpCandList. On the other hand, when a block is encoded/decoded basedon an affine motion model, a prediction region merge candidate mvAfC andderived based on the block may be added to a prediction region affinemotion information list HmvpAfCandList.

Affine seed vectors of a block encoded/decoded based on the affinemotion model may be stored in a prediction region merge candidatederived from the block. Accordingly, the prediction region mergecandidate may be used as a merge candidate for deriving the affine seedvector of the current block.

In addition to the prediction region motion information list describedabove, an additional prediction region motion information list may bedefined. In addition to the prediction region motion information listdescribed above (hereinafter, referred to as a first prediction regionmotion information list), a long-term motion information list(hereinafter, referred to as a second prediction region motioninformation list) may be defined. Here, the long-term motion informationlist includes long-term merge candidates.

When both the first prediction region motion information list and thesecond prediction region motion information list are empty, first,prediction region merge candidates may be added to the second predictionregion motion information list. Only after the number of availableprediction region merge candidates reaches the maximum number in thesecond prediction region motion information list, prediction regionmerge candidates may be added to the first prediction region motioninformation list.

Alternatively, one inter prediction merge candidate may be added to boththe second prediction region motion information list and the firstprediction region motion information list.

At this point, the second prediction region motion information list, theconfiguration of which has been completed, may not be updated any more.Alternatively, when the decoded region is greater than or equal to apredetermined ratio of the slice, the second prediction region motioninformation list may be updated. Alternatively, the second predictionregion motion information list may be updated for every N coding treeunit lines.

On the other hand, the first prediction region motion information listmay be updated whenever a block encoded/decoded by inter prediction isgenerated. However, it may be set not to use the prediction region mergecandidate added to the second prediction region motion information list,to update the first prediction region motion information list.

Information for selecting any one among the first prediction regionmotion information list and the second prediction region motioninformation list may be signaled through a bitstream. When the number ofmerge candidates included in the merge candidate list is smaller than athreshold value, merge candidates included in the prediction regionmotion information list indicated by the information may be added to themerge candidate list.

Alternatively, a prediction region motion information list may beselected based on the size and shape of the current block, interprediction mode, whether bidirectional prediction is enabled, whethermotion vector refinement is enabled, or whether triangular partitioningis enabled.

Alternatively, although a prediction region merge candidate included inthe first prediction region motion information list is added, when thenumber of merge candidates included in the merge candidate list issmaller than the maximum number of merges, the prediction region mergecandidates included in the second prediction region motion informationlist may be added to the merge candidate list.

FIG. 22 is a view showing an example in which a prediction region mergecandidate included in a long-term motion information list is added to amerge candidate list.

When the number of merge candidates included in the merge candidate listis smaller than the maximum number, the prediction region mergecandidates included in the first prediction region motion informationlist HmvpCandList may be added to the merge candidate list. When thenumber of merge candidates included in the merge candidate list issmaller than the maximum number although the prediction region mergecandidates included in the first prediction region motion informationlist are added to the merge candidate list, the prediction region mergecandidates included in the long-term motion information listHmvpLTCandList may be added to the merge candidate list.

Table 2 shows a process of adding the prediction region merge candidatesincluded in the long-term motion information list to the merge candidatelist.

TABLE 2 For each candidate in HMVPCandList with index HMVPLTIdx = 1 . .. numHMVPLTCand, the following ordered steps are repeated until combStopis equal to true - sameMotion is set to FALSE - If hmvpStop is equal toFALSE and numCurrMergecand is less than (MaxNumMergeCand- 1), hmvpLT isset to TRUE - If HMVPLTCandList[NumLTHmvp-HMVPLTIdx] have the samemotion vectors and the same reference indices with any mergeCandList[i]with I being 0 . . . numOrigMergeCand-1 and HasBeenPruned[i] equal tofalse, sameMotion is set to true - If sameMotion is equal to false,mergeCandList[numCurrMergeCand++] is set toHMVPLTCandList[NumLTHmvp-HMVPLTIdx] - If numCurrMergeCand is equal to(MaxNumMergeCand-1), hmvpLTStop is set to TRUE

The prediction region merge candidate may be set to include additionalinformation, in addition to motion information. For example, for theprediction region merge candidate, a size, a shape, or partitioninformation of a block may be additionally stored. When the mergecandidate list of the current block is constructed, only interprediction merge candidates having a size, a shape, or partitioninformation the same as or similar to those of the current block areused among the inter prediction merge candidates, or inter predictionmerge candidates having a size, a shape, or partition information thesame as or similar to those of the current block may be added to themerge candidate list in the first place.

Alternatively, a prediction region motion information list may begenerated for each of the size, shape, or partition information of ablock. Among the plurality of prediction region motion informationlists, a merge candidate list of the current block may be generated byusing a prediction region motion information list corresponding to theshape, size, or partition information of the current block.

When the number of merge candidates included in the merge candidate listof the current block is smaller than the threshold value, the predictionregion merge candidates included in the prediction region motioninformation list may be added to the merge candidate list. The additionprocess is performed in an ascending or descending order based on theindex. For example, a prediction region merge candidate having thelargest index may be first added to the merge candidate list.

When it is desired to add a prediction region merge candidate includedin the prediction region motion information list to the merge candidatelist, a redundancy check may be performed between the prediction regionmerge candidate and the merge candidates previously stored in the mergecandidate list.

For example, Table 3 shows a process in which a prediction region mergecandidate is added to the merge candidate list.

TABLE 3 For each candidate in HMVPCandList with index HMVPIdx = 1 . . .numCheckedHMVPCand, the following ordered steps are repeated untilcombStop is equal to true - sameMotion is set to false - IfHMVPCandList[NumHmvp-HMVPIdx] have the same motion vectors and the samereference indices with any mergeCandList[i] with I being 0 . . .numOrigMergeCand-1 and HasBeenPruned[i] equal to false, sameMotion isset to true - If sameMotion is equal to false,mergeCandList[numCurrMergeCand++] is set toHMVPCandList[NumHmvp-HMVPIdx] - If numCurrMergeCand is equal to(MaxNumMergeCand-1), hmvpStop is set to TRUE

The redundancy check may be performed only on some of the predictionregion merge candidates included in the prediction region motioninformation list. For example, the redundancy check may be performedonly on prediction region merge candidates having an index larger than athreshold value or smaller than a threshold value. Alternatively, theredundancy check may be performed only on N merge candidates having thelargest index or N merge candidates having the smallest index.

Alternatively, the redundancy check may be performed only on some of themerge candidates previously stored in the merge candidate list. Forexample, the redundancy check may be performed only on a merge candidatehaving an index larger than a threshold value or smaller than athreshold value, or on a merge candidate derived from a block at aspecific position. Here, the specific position may include at least oneamong a left neighboring block, a top neighboring block, a top-rightneighboring block, and a bottom-left neighboring block of the currentblock.

FIG. 23 is a view showing an example in which a redundancy check isperformed only on some of merge candidates.

When it is desired to add the prediction region merge candidateHmvpCand[j] to the merge candidate list, a redundancy check may beperformed on the prediction region merge candidate with two mergecandidates mergeCandList[NumMerge−2] and mergeCandList[NumMerge−1]having the largest indexes. Here, NumMerge may represent the number ofspatial merge candidates and temporal merge candidates that areavailable.

Unlike the example shown in the drawing, when it is desired to add aprediction region merge candidate HmvpCand[j] to the merge candidatelist, a redundancy check may be performed on the prediction region mergecandidate with up to two merge candidates having the smallest index. Forexample, it is possible to check whether mergeCandList[0] andmergeCandList[1] are the same as HmvpCand[j].

Alternatively, a redundancy check may be performed only on mergecandidates derived at a specific position. For example, the redundancycheck may be performed on at least one among a merge candidate derivedfrom a neighboring block positioned on the left side of the currentblock and a merge candidate derived from a neighboring block positionedon the top the current block. When a merge candidate derived at aspecific position does not exist in the merge candidate list, aprediction region merge candidate may be added to the merge candidatelist without having a redundancy check.

When it is desired to add the prediction region merge candidateHmvpCand[j] to the merge candidate list, a redundancy check may beperformed on the prediction region merge candidate with two mergecandidates mergeCandList[NumMerge−2] and mergeCandList[NumMerge−1]having the largest indexes. Here, NumMerge may represent the number ofspatial merge candidates and temporal merge candidates that areavailable.

The redundancy check with the merge candidate may be performed only onsome of the prediction region merge candidates. For example, theredundancy check may be performed only on N prediction region mergecandidates having a large index or N prediction region merge candidateshaving a small index among the prediction region merge candidatesincluded in the prediction region motion information list. For example,the redundancy check may be performed only on prediction region mergecandidates of which a difference between the number of prediction regionmerge candidates included in the prediction region motion informationlist and an index is smaller than or equal to a threshold value. Whenthe threshold value is 2, the redundancy check may be performed only onthree prediction region merge candidates having the largest index valueamong the prediction region merge candidates included in the predictionregion motion information list. The redundancy check may be omitted forprediction region merge candidates excluding the three prediction regionmerge candidates. When the redundancy check is omitted, a predictionregion merge candidate may be added to the merge candidate listregardless of whether the prediction region merge candidate has motioninformation the same as that of the merge candidate.

Contrarily, it may be set to perform the redundancy check only onprediction region merge candidates of which a difference between thenumber of prediction region merge candidates included in the predictionregion motion information list and an index is equal to or greater thana threshold value.

The number of prediction region merge candidates on which the redundancycheck is performed may be predefined in the encoder and the decoder. Forexample, the threshold value may be an integer such as 0, 1 or 2.

Alternatively, the threshold value may be determined based on at leastone among the number of merge candidates included in the merge candidatelist and the number of prediction region merge candidates included inthe prediction region motion information list.

When a merge candidate the same as the first prediction region mergecandidate is found and a redundancy check is performed on the secondprediction region merge candidate, the redundancy check with a mergecandidate the same as the first prediction region merge candidate may beomitted.

FIG. 24 is a view showing an example in which a redundancy check isomitted for a specific merge candidate.

When it is desired to add a prediction region merge candidateHmvpCand[i] having index i to the merge candidate list, a redundancycheck is performed between the prediction region merge candidate andmerge candidates previously stored in the merge candidate list. At thispoint, when a merge candidate mergeCandList[j] the same as theprediction region merge candidate HmvpCand[i] is found, the redundancycheck may be performed between the prediction region merge candidateHmvpCand[i−1] having index i−1 and the merge candidates without addingthe prediction region merge candidate HmvpCand[i] to the merge candidatelist. At this point, the redundancy check between the prediction regionmerge candidate HmvpCand[i−1] and the merge candidate mergeCandList[j]may be omitted.

For example, in the example shown in FIG. 24, it is determined thatHmvpCand[i] and mergeCandList[2] are the same. Accordingly, HmvpCand[i]is not added to the merge candidate list, and a redundancy check may beperformed on HmvpCand[i−1]. At this point, the redundancy check betweenHvmpCand[i−1] and mergeCandList[2] may be omitted.

When the number of merge candidates included in the merge candidate listof the current block is smaller than the threshold value, at least oneamong a pairwise merge candidate and a zero-merge candidate may befurther included, in addition to the prediction region merge candidate.The pairwise merge candidate means a merge candidate having an averagevalue of motion vectors of two or more merge candidates as a motionvector, and the zero-merge candidate means a merge candidate having amotion vector of 0.

A merge candidate may be added to the merge candidate list of thecurrent block in the following order.

Spatial merge candidate—Temporal merge candidate—Prediction region mergecandidate—(Prediction region affine merge candidate)—Pairwise mergecandidate—Zero merge candidate

The spatial merge candidate means a merge candidate derived from atleast one among a neighboring block and a non-neighboring block, and thetemporal merge candidate means a merge candidate derived from a previousreference picture. The prediction region affine merge candidaterepresents a prediction region merge candidate derived from a blockencoded/decoded with an affine motion model.

The prediction region motion information list may also be used in themotion vector prediction mode. For example, when the number of motionvector prediction candidates included in a motion vector predictioncandidate list of the current block is smaller than a threshold value, aprediction region merge candidate included in the prediction regionmotion information list may be set as a motion vector predictioncandidate for the current block. Specifically, the motion vector of theprediction region merge candidate may be set as a motion vectorprediction candidate.

When any one among the motion vector prediction candidates included inthe motion vector prediction candidate list of the current block isselected, the selected candidate may be set as the motion vectorpredictor of the current block. Thereafter, after a motion vectorresidual coefficient of the current block is decoded, a motion vector ofthe current block may be obtained by adding the motion vector predictorand the motion vector residual coefficient.

The motion vector prediction candidate list of the current block may beconfigured in the following order.

Spatial motion vector prediction candidate—Temporal motion vectorprediction candidate—Inter prediction region merge candidate—(Interprediction region affine merge candidate)—Zero-motion vector predictioncandidate

The spatial motion vector prediction candidate means a motion vectorprediction candidate derived from at least one among a neighboring blockand a non-neighboring block, and the temporal motion vector predictioncandidate means a motion vector prediction candidate derived from aprevious reference picture. The prediction region affine merge candidaterepresents a prediction region motion vector prediction candidatederived from a block encoded/decoded with the affine motion model. Thezero-motion vector prediction candidate represents a candidate having amotion vector value of 0.

A merge processing area having a size greater than that of a codingblock may be defined. Coding blocks included in the merge processingarea are not sequentially encoded/decoded, and may be processed inparallel. Here, that coding blocks are not sequentially encoded/decodedmeans that an encoding/decoding order is not defined. Accordingly, aprocess of encoding/decoding the blocks included in the merge processingarea may be independently processed. Alternatively, the blocks includedin the merge processing area may share merge candidates. Here, the mergecandidates may be derived based on the merge processing area.

According to the characteristics described above, the merge processingarea may also be referred to as a parallel processing region, a sharedmerge region (SMR), or a merge estimation region (MER).

The merge candidate of the current block may be derived based on thecoding block. However, when the current block is included in a mergeprocessing area of a size greater than the current block, a candidateblock included in the merge processing area the same as the currentblock may be set to be unavailable as a merge candidate.

FIG. 25 is a view showing an example in which candidate blocks includedin the same merge processing area as the current block are set to beunavailable as a merge candidate.

In the example shown in FIG. 25 (a), when CU5 is encoded/decoded, blocksincluding reference samples adjacent to CU5 may be set as candidateblocks. At this point, candidate blocks X3 and X4 included in the mergeprocessing area the same as CU5 may be set to be unavailable as a mergecandidate of CU5. On the other hand, candidate blocks X0, X1 and X2 thatare not included in the merge processing area the same as CU5 may be setto be available as a merge candidate.

In the example shown in FIG. 25(b), when CU8 is encoded/decoded, blocksincluding reference samples adjacent to CU8 may be set as candidateblocks. At this point, candidate blocks X6, X7 and X8 included in themerge processing area the same as CU8 may be set to be unavailable as amerge candidate. On the other hand, candidate blocks X5 and X9 that arenot included in the merge processing area the same as CU8 may be set tobe available as a merge candidate.

The merge processing area may be a square or non-square shape.Information for determining the merge processing area may be signaledthrough a bitstream. The information may include at least one amonginformation indicating the shape of the merge processing area andinformation indicating the size of the merge processing area. When themerge processing area is a non-square shape, at least one amonginformation indicating the size of the merge processing area,information indicating the width and/or height of the merge processingarea, and information indicating a ratio of width to height of the mergeprocessing area may be signaled through a bitstream.

The size of the merge processing area may be determined based on atleast one among information signaled through a bitstream, a pictureresolution, a slice size, and a tile size.

When motion compensation prediction is performed on a block included inthe merge processing area, a prediction region merge candidate derivedbased on motion information of the block on which motion compensationprediction has been performed may be added to the prediction regionmotion information list.

However, in the case where a prediction region merge candidate derivedfrom a block included in the merge processing area is added to theprediction region motion information list, when another block in themerge processing area, which actually is encoded/decoded after the blockis encoded/decoded, is encoded/decoded, there may be a case of using aprediction region merge candidate derived from the block. That is,although dependency among blocks should be excluded when the blocksincluded in the merge processing area are encoded/decoded, there may bea case a case of performing motion prediction compensation using motioninformation of another block included in the merge processing area. Inorder to solve the problem, although encoding/decoding of a blockincluded in the merge processing area is completed, motion informationof the encoded/decoded block may not be added to the prediction regionmotion information list.

Alternatively, when motion compensation prediction is performed on theblocks included in the merge processing area, prediction region mergecandidates derived from the blocks may be added to the prediction regionmotion information list in a predefined order. Here, the predefinedorder may be determined according to the scan order of the coding blocksin the merge processing area or the coding tree unit. The scan order maybe at least one among the raster scan, horizontal scan, vertical scan,and zigzag scan. Alternatively, the predefined order may be determinedbased on motion information of each block or the number of blocks havingthe same motion information.

Alternatively, a prediction region merge candidate includingunidirectional motion information may be added to the prediction regionmerge list before a prediction region merge candidate includingbidirectional motion information. Contrarily, a prediction region mergecandidate including bidirectional motion information may be added to theprediction region merge candidate list before a prediction region mergecandidate including unidirectional motion information.

Alternatively, a prediction region merge candidate may be added to theprediction region motion information list according to an order of ahigh use frequency or a low use frequency within the merge processingarea or the coding tree unit.

When the current block is included in the merge processing area and thenumber of merge candidates included in the merge candidate list of thecurrent block is smaller than the maximum number, prediction regionmerge candidates included in the prediction region motion informationlist may be added to the merge candidate list. At this point, it may beset not to add a prediction region merge candidate derived from a blockincluded in a merge processing area the same as the current block to themerge candidate list of the current block.

Alternatively, when the current block is included in the mergeprocessing area, it may be set not to use the prediction region mergecandidates included in the prediction region motion information list.That is, although the number of merge candidates included in the mergecandidate list of the current block is smaller than the maximum number,the prediction region merge candidates included in the prediction regionmotion information list may not be added to the merge candidate list.

A prediction region motion information list for a merge processing areaor a coding tree unit may be configured. This prediction region motioninformation list performs a function of temporarily storing motioninformation of blocks included in the merge processing area. In order todistinguish a general prediction region motion information list from theprediction region motion information list for a merge processing area ora coding tree unit, the prediction region motion information list for amerge processing area or a coding tree unit is referred to as atemporary motion information list. In addition, a prediction regionmerge candidate stored in the temporary motion information list will bereferred to as a temporary merge candidate.

FIG. 26 is a view showing a temporary motion information list.

A temporary motion information list for a coding tree unit or a mergeprocessing area may be configured. When motion compensation predictionhas been performed on the current block included in the coding tree unitor the merge processing area, motion information of the block may not beadded to the inter prediction motion information list HmvpCandList.Instead, a temporary merge candidate derived from the block may be addedto the temporary motion information list HmvpMERCandList. That is, thetemporary merge candidate added to the temporary motion information listmay not be added to the prediction region motion information list.Accordingly, the prediction region motion information list may notinclude prediction region merge candidates derived based on motioninformation of the blocks included in the coding tree unit or the mergeprocessing area.

The maximum number of merge candidates that the temporary motioninformation list may include may be set to be the same as that of theprediction region motion information list. Alternatively, the maximumnumber of merge candidates that the temporary motion information listmay include may be determined according to the size of the coding treeunit or the merge processing area.

The current block included in the coding tree unit or the mergeprocessing area may be set not to use the temporary motion informationlist for a corresponding coding tree unit or a corresponding mergeprocessing area. That is, when the number of merge candidates includedin the merge candidate list of the current block is smaller than athreshold value, the prediction region merge candidates included in theprediction region motion information list are added to the mergecandidate list, and the temporary merge candidates included in thetemporary motion information list may not be added to the mergecandidate list. Accordingly, motion information of other blocks includedin the coding tree unit or the merge processing area the same as thecurrent block may not be used for motion compensation prediction of thecurrent block.

When encoding/decoding of all the blocks included in the coding treeunit or the merge processing area is completed, the prediction regionmotion information list and the temporary motion information list may bemerged.

FIG. 27 is a view showing an example of merging a prediction regionmotion information list and a temporary motion information list.

When coding/decoding of all the blocks included in the coding tree unitor the merge processing area is completed, as shown in the example ofFIG. 27, the prediction region motion information list may be updatedwith the temporary merge candidates included in the temporary motioninformation list.

At this point, the temporary merge candidates included in the temporarymotion information list may be added to the prediction region motioninformation list in order of the temporary merge candidates inserted inthe temporary motion information list (i.e., in ascending or descendingorder of index values).

As another example, the temporary merge candidates included in thetemporary motion information list may be added to the prediction regionmotion information list in a predefined order.

Here, the predefined order may be determined according to the scan orderof the coding blocks in the merge processing area or the coding treeunit. The scan order may be at least one among the raster scan,horizontal scan, vertical scan, and zigzag scan. Alternatively, thepredefined order may be determined based on motion information of eachblock or the number of blocks having the same motion information.

Alternatively, a temporary merge candidate including unidirectionalmotion information may be added to the prediction region merge listbefore a temporary merge candidate including bidirectional motioninformation. Contrarily, a temporary merge candidate includingbidirectional motion information may be added to the prediction regionmerge candidate list before a temporary merge candidate includingunidirectional motion information.

Alternatively, a temporary merge candidate may be added to theprediction region motion information list according to an order of ahigh use frequency or a low use frequency within the merge processingarea or the coding tree unit.

When a temporary merge candidate included in the temporary motioninformation list is added to the prediction region motion informationlist, a redundancy check may be performed on the temporary mergecandidate. For example, when a prediction region merge candidate thesame as the temporary merge candidate included in the temporary motioninformation list is previously stored in the prediction region motioninformation list, the temporary merge candidate may not be added to theprediction region motion information list. At this point, a redundancycheck may be performed on some of the prediction region merge candidatesincluded in the prediction region motion information list. For example,the redundancy check may be performed on inter prediction mergecandidates having an index larger than a threshold value or smaller thana threshold value. For example, when the temporary merge candidate isthe same as a prediction region merge candidate having an index largerthan or equal to a predefined value, the temporary merge candidate maynot be added to the prediction region motion information list.

A prediction region merge candidate derived from a block included in acoding tree unit or a merge processing area the same as those of thecurrent block may be limited from being used as a merge candidate of thecurrent block. To this end, address information of a block may beadditionally stored for the prediction region merge candidate. Theaddress information of the block may include one among the location ofthe block, the address of the block, the index of the block, thelocation of the merge processing area including the block, the addressof the merge processing area including the block, the index of the mergeprocessing area including the block, the location of the coding treeregion including the block, the address of the coding tree regionincluding the block, and the index of the coding tree region includingthe block.

FIGS. 28 and 29 are views showing an example in which an encoding regionmerge candidate includes address information of a block.

Motion information of a block encoded by inter prediction may be storedas motion information of an encoding region merge candidate. Forexample, a motion vector my of a block may be stored as a motion vectormvCand of an encoding region merge candidate, and a reference pictureindex RefIdx of a block may be stored as a reference picture indexRefIdxCand of an encoding region merge candidate.

Additionally, address information of a block may be further stored forthe encoding region merge candidate. For example, the address BLK_ADR ofa block, the address MER_ADDR of a merge processing area including theblock, or the address CTU_ADDR of a coding tree unit including the blockmay be additionally stored.

In the example shown in FIG. 28, it is shown that the motion vectormvCand, the reference picture index RefIdxCand, and the address MER_ADDRof the merge processing area are stored for the encoding region mergecandidate.

A plurality of address information may be stored for the encoding regionmerge candidate. In the example shown in FIG. 29, it is shown that themotion vector mvCand, the reference picture index RefIdxCand, theaddress MER_ADDR of the merge processing area, and the address CTU_ADDRof the coding tree unit are stored for the encoding region mergecandidate.

Whether the encoding region merge candidate can be used as a mergecandidate of the current block may be determined by comparing theaddress of the current block with the address of the encoding regionmerge candidate. For example, when the index of the merge processingarea including the current block and the index of the merge processingarea indicated by the encoding region merge candidate is the same, theencoding region merge candidate may be set to be unavailable as a mergecandidate of the current block. Alternatively, when the index of thecoding tree region including the current block is the same as the indexof the coding tree region indicated by the encoding region mergecandidate, the encoding region merge candidate may be set to beunavailable as a merge candidate of the current block. That is, anencoding region merge candidate derived from a block included in a mergeprocessing area or a coding tree unit the same as those of the currentblock, or an encoding region merge candidate derived from a blockadjacent to the current block may not be added to the merge candidatelist of the current block.

FIGS. 30 and 31 are views showing an example in which an encoding regionmerge candidate having address information the same as that of thecurrent block is set to be unavailable as a merge candidate of thecurrent block.

When the index of a merge processing area to which the current blockbelongs is 2, an encoding region merge candidate derived from a blockbelonging to the merge processing area of index 2 may be set to beunavailable as a merge candidate of the current block. In the exampleshown in FIG. 30, since address information of the encoding region mergecandidate HvmpCand[5] of index 5 indicates index 2, the encoding regionmerge candidate may be set to be unavailable as a merge candidate of thecurrent block.

When the index of the coding tree unit to which the current blockbelongs is 2 and the index of the merge processing area to which thecurrent block belongs is 1, an encoding region merge candidate derivedfrom a block included in a coding tree unit and a merge processing areathe same as those of the current block may be set to be unavailable as amerge candidate of the current block. In the example shown in FIG. 31,in the case of the encoding region merge candidate HvmpCand[5] of whichthe index is 5, since the index of the coding tree unit indicates 2 andthe index of the merge processing area indicates 1, the encoding regionmerge candidate may be set to be unavailable as a merge candidate of thecurrent block.

As another example, when the difference between the address informationindicated by the encoding region merge candidate and the addressinformation of the current block is greater than or equal to a thresholdvalue, the encoding region merge candidate may be set as unavailable.For example, when the difference between the address or index of thecoding tree unit indicated by the encoding region merge candidate andthe address or index of the coding tree unit to which the current blockbelongs is greater than or equal to a threshold value, the encodingregion merge candidate may be set as unavailable.

Alternatively, as another example, when the difference between theaddress information indicated by the encoding region merge candidate andthe address information of the current block is smaller than or equal toa threshold value, the encoding region merge candidate may be set asunavailable. For example, when the difference between the address orindex indicated by the encoding region merge candidate and the addressor index of the current block is smaller than or equal to a thresholdvalue, the encoding region merge candidate may be set as unavailable.That is, an encoding region merge candidate derived from a blockadjacent to the current block may be set to be unavailable as a mergecandidate of the current block.

When an encoding region merge candidate derived from the current blockis to be added to an encoding region motion information list, aredundancy check may be performed. At this point, the redundancy checkmay be determining whether motion information and address information ofthe encoding region merge candidate derived from the current block arethe same as those of an encoding region merge candidate previouslystored in the encoding region motion information list. For example, whenan encoding region merge candidate having a motion vector, a referencepicture index, and address information the same as those of the encodingregion merge candidate derived from the current block is previouslystored, the encoding region merge candidate derived from the currentblock may not be added to the encoding region motion information list.Alternatively, when an encoding region merge candidate having a motionvector, a reference picture index, and address information the same asthose of the encoding region merge candidate derived from the currentblock is previously stored, the previously stored encoding region mergecandidate may be deleted, and the encoding region merge candidatederived from the current block may be added to the encoding regionmotion information list. At this point, a largest index or a smallestindex may be assigned to the encoding region merge candidate derivedfrom the current block.

Alternatively, it may be set not to consider whether the addressinformation is the same when the redundancy check is performed. Forexample, although address information of an encoding region mergecandidate derived from the current block is different from the addressinformation of an encoding region merge candidate previously stored inthe encoding region motion information list, when the motion informationof both the encoding region merge candidates is the same, the encodingregion merge candidate derived from the current block may not be addedto the encoding region motion information list. Alternatively, whenalthough the address information of the encoding region merge candidatederived from the current block is the same as the motion information(→address information) of the encoding region merge candidate previouslystored in the encoding region motion information list, the addressinformation (→motion information) is different, the previously storedencoding region merge candidate may be deleted, and the encoding regionmerge candidate derived from the current block may be added to theencoding region motion information list. At this point, a largest indexor a smallest index may be assigned to the encoding region mergecandidate derived from the current block.

Intra prediction is for predicting a current block using reconstructedsamples that have been encoded/decoded around the current block. At thispoint, samples reconstructed before an in-loop filter is applied may beused for intra prediction of the current block.

The intra prediction technique includes matrix-based intra prediction,and general intra prediction considering directionality with respect toneighboring reconstructed samples. Information indicating the intraprediction technique of the current block may be signaled through abitstream. The information may be a 1-bit flag. Alternatively, the intraprediction technique of the current block may be determined based on atleast one among the location, the size, and the shape of the currentblock, or based on an intra prediction technique of a neighboring block.For example, when the current block exists across a picture boundary, itmay be set not to apply the matrix-based intra prediction intraprediction to the current block.

The matrix-based intra prediction intra prediction is a method ofacquiring a prediction block of the current block by an encoder and adecoder based on a matrix product between a previously stored matrix andreconstructed samples around the current block. Information forspecifying any one among a plurality of previously stored matrixes maybe signaled through a bitstream. The decoder may determine a matrix forintra prediction of the current block based on the information and thesize of the current block.

The general intra prediction is a method of acquiring a prediction blockfor the current block based on a non-angular intra prediction mode or anangular intra prediction mode.

A derived residual video may be derived by subtracting a predictionvideo from an original video. At this point, when the residual video ischanged to the frequency domain, subjective video quality of the videois not significantly lowered although the high-frequency componentsamong the frequency components are removed. Accordingly, when values ofthe high-frequency components are converted to be small or the values ofthe high-frequency components are set to 0, there is an effect ofincreasing the compression efficiency without generating significantvisual distortion. By reflecting this characteristic, the current blockmay be transformed to decompose a residual video into two-dimensionalfrequency components. The transform may be performed using a transformtechnique such as Discrete Cosine Transform (DST) or Discrete SineTransform (DST).

After the current block is transformed using DCT or DST, the transformedcurrent block may be transformed again. At this point, the transformbased on DCT or DST may be defined as a first transform, andtransforming again a block to which the first transform is applied maybe defined as a second transform.

The first transform may be performed using any one among a plurality oftransform core candidates. For example, the first transform may beperformed using any one among DCT2, DCT8, or DCT7.

Different transform cores may be used for the horizontal direction andthe vertical direction. Information indicating combination of atransform core of the horizontal direction and a transform core of thevertical direction may be signaled through a bitstream.

Units for performing the first transform and the second transform may bedifferent. For example, the first transform may be performed on an 8×8block, and the second transform may be performed on a subblock of a 4×4size among the transformed 8×8 block. At this point, the transformcoefficients of the residual regions that has not been performed thesecond transform may be set to 0.

Alternatively, the first transform may be performed on a 4×4 block, andthe second transform may be performed on a region of an 8×8 sizeincluding the transformed 4×4 block.

Information indicating whether the second transform has been performedmay be signaled through a bitstream.

The decoder may perform an inverse transform of the second transform (asecond inverse transform), and may perform an inverse transform of thefirst transform (a first inverse transform) as a result of the inversetransform. As a result of performing the second inverse transform andthe first inverse transform, residual signals for the current block maybe acquired.

Quantization is for reducing the energy of a block, and the quantizationprocess includes a process of dividing a transform coefficient by aspecific constant value. The constant value may be derived by aquantization parameter, and the quantization parameter may be defined asa value between 1 and 63.

When the encoder performs transform and quantization, the decoder mayacquire a residual block through inverse quantization and inversetransform. The decoder may acquire a reconstructed block for the currentblock by adding a prediction block and the residual block.

When a reconstructed block of the current block is acquired, loss ofinformation occurring in the quantization and encoding process may bereduced through in-loop filtering. An in-loop filter may include atleast one among a deblocking filter, a sample adaptive offset filter(SAO), and an adaptive loop filter (ALF).

Applying the embodiments described above focusing on a decoding processor an encoding process to an encoding process or a decoding process isincluded in the scope of the present disclosure. Changing theembodiments described in a predetermined order in an order differentfrom the described order is also included in the scope of the presentdisclosure.

Although the embodiments above have been described based on a series ofsteps or flowcharts, this does not limit the time series order of thepresent disclosure, and may be performed simultaneously or in adifferent order as needed. In addition, each of the components (e.g.,units, modules, etc.) constituting the block diagram in the embodimentsdescribed above may be implemented as a hardware device or software, ora plurality of components may be combined to be implemented as a singlehardware device or software. The embodiments described above may beimplemented in the form of program commands that can be executed throughvarious computer components and recorded in a computer-readablerecording medium. The computer-readable recording medium may includeprogram commands, data files, data structures and the like independentlyor in combination. The computer-readable recording medium includes, forexample, magnetic media such as a hard disk, a floppy disk and amagnetic tape, optical recording media such as a CD-ROM and a DVD,magneto-optical media such as a floptical disk, and hardware devicesspecially configured to store and execute program commands, such as aROM, a RAM, a flash memory and the like. The hardware devices describedabove can be configured to operate using one or more software modules toperform the process of the present disclosure, and vice versa.

The present disclosure can be applied to an electronic device thatencodes and decodes a video.

What is claimed is:
 1. A video decoding method, comprising: deriving amerge candidate for a current block from a neighboring block of thecurrent block; adding the derived merge candidate to a merge candidatelist; adding at least one prediction region merge candidate derivedbased on motion information of the neighboring block included in aprediction region motion information list to the merge candidate listwhen a number of merge candidates added to the merge candidate list issmaller than a first threshold value; wherein the prediction regionmerge candidate included in the prediction region motion informationlist is obtained by determining whether the neighboring block isincluded in a predetermined region, wherein the predetermined region isa merge processing area; when it is determined that the neighboringblock is not included in the predetermined region, the prediction regionmerge candidate is added to the prediction region motion informationlist; and/or when it is determined that the neighboring block isincluded in the predetermined region, the prediction region mergecandidate is not added to the prediction region motion information list;deriving motion information for the current block based on the mergecandidate list; and performing motion compensation for the current blockbased on the derived motion information, wherein whether to add theprediction region merge candidate to the merge candidate list isdetermined based on a result of comparison between motion information ofthe prediction region merge candidate and motion information of a mergecandidate included in the merge candidate list.
 2. The method accordingto claim 1, wherein the comparison is performed on at least one mergecandidate in the merge candidate list, of which an index is smaller thanor equal to a second threshold value.
 3. The method according to claim1, wherein the comparison is performed on a merge candidate derived froma block at a specific position.
 4. The method according to claim 1,wherein the comparison is performed on at least one among a mergecandidate derived from a left neighboring block positioned on a leftside of the current block and a merge candidate derived from a topneighboring block positioned on a top of the current block.
 5. Themethod according to claim 1, wherein when it is determined that there isa merge candidate in the merge candidate list having motion informationthe same as that of a first prediction region merge candidate, the firstprediction region merge candidate is not added to the merge candidatelist, and whether to add to a second prediction region merge candidateto the merge candidate list is determined based on a result ofcomparison between motion information of the second prediction regionmerge candidate included in the prediction region motion informationlist and motion information of the merge candidate included in the mergecandidate list.
 6. The method according to claim 5, whereindetermination on whether the second prediction region merge candidatehas motion information the same as that of a merge candidate havingmotion information the same as that of the first prediction region mergecandidate is omitted.
 7. The method according to claim 1, wherein thecomparison is performed on the prediction region merge candidate havingan index larger than a second threshold value.
 8. The method accordingto claim 1, further comprising: when a size of the neighboring block isno smaller than a preset size, adding the prediction region mergecandidate derived based on motion information of the neighboring blockto the prediction region motion information list; or when the size ofthe neighboring block is smaller than the preset size, not adding theprediction region merge candidate derived based on motion information ofthe neighboring block to the prediction region motion information list.9. The method according to claim 8, further comprising: adding theprediction region merge candidate derived based on motion information ofthe neighboring block included in the prediction region motioninformation list to the merge candidate list when the number of mergecandidates added to the merge candidate list is smaller than the firstthreshold value.
 10. A video encoding method, comprising: deriving amerge candidate for a current block from a neighboring block of thecurrent block; adding the derived merge candidate to a merge candidatelist; adding at least one prediction region merge candidate derivedbased on motion information of the neighboring block included in aprediction region motion information list to the merge candidate listwhen a number of merge candidates added to the merge candidate list issmaller than a first threshold value; wherein the prediction regionmerge candidate included in the prediction region motion informationlist is obtained by determining whether the neighboring block isincluded in a predetermined region, wherein the predetermined region isa merge processing area; when it is determined that the neighboringblock is not included in the predetermined region, the prediction regionmerge candidate is added to the prediction region motion informationlist; and/or when it is determined that the neighboring block isincluded in the predetermined region, the prediction region mergecandidate is not added to the prediction region motion information list;deriving motion information for the current block based on the mergecandidate list; and performing motion compensation for the current blockbased on the derived motion information, wherein whether to add theprediction region merge candidate to the merge candidate list isdetermined based on a result of comparison between motion information ofthe prediction region merge candidate and motion information of a mergecandidate included in the merge candidate list.
 11. The method accordingto claim 10, wherein the comparison is performed on at least one mergecandidate in the merge candidate list, of which an index is smaller thanor equal to a second threshold value.
 12. The method according to claim10, wherein the comparison is performed on a merge candidate derivedfrom a block at a specific position.
 13. The method according to claim10, wherein the comparison is performed on at least one among a mergecandidate derived from a left neighboring block positioned on a leftside of the current block and a merge candidate derived from a topneighboring block positioned on a top of the current block.
 14. Themethod according to claim 10, wherein when it is determined that thereis a merge candidate in the merge candidate list having motioninformation the same as that of a first prediction region mergecandidate, the first prediction region merge candidate is not added tothe merge candidate list, and whether to add to a second predictionregion merge candidate to the merge candidate list is determined basedon a result of comparison between motion information of the secondprediction region merge candidate included in the prediction regionmotion information list and motion information of the merge candidateincluded in the merge candidate list.
 15. The method according to claim14, wherein determination on whether the second prediction region mergecandidate has motion information the same as that of a merge candidatehaving motion information the same as that of the first predictionregion merge candidate is omitted.
 16. The method according to claim 10,wherein the comparison is performed on the prediction region mergecandidate having an index larger than a second threshold value.
 17. Themethod according to claim 10, further comprising: when a size of theneighboring block is no smaller than a preset size, adding theprediction region merge candidate derived based on motion information ofthe neighboring block to the prediction region motion information list;or when the size of the neighboring block is smaller than the presetsize, not adding the prediction region merge candidate derived based onmotion information of the neighboring block to the prediction regionmotion information list.
 18. The method according to claim 17, furthercomprising: adding the prediction region merge candidate derived basedon motion information of the neighboring block included in theprediction region motion information list to the merge candidate listwhen the number of merge candidates added to the merge candidate list issmaller than the first threshold value.
 19. A video decoding apparatuscomprising an inter prediction part for: deriving a merge candidate fora current block from a neighboring block of the current block; addingthe derived merge candidate to a merge candidate list; adding at leastone prediction region merge candidate derived based on motioninformation of the neighboring block included in a prediction regionmotion information list to the merge candidate list when a number ofmerge candidates added to the merge candidate list is smaller than afirst threshold value; wherein the prediction region merge candidateincluded in the prediction region motion information list is obtained bydetermining whether the neighboring block is included in a predeterminedregion, wherein the predetermined region is a merge processing area;when it is determined that the neighboring block is not included in thepredetermined region, the prediction region merge candidate is added tothe prediction region motion information list; and/or when it isdetermined that the neighboring block is included in the predeterminedregion, the prediction region merge candidate is not added to theprediction region motion information list; deriving motion informationfor the current block based on the merge candidate list; and performingmotion compensation for the current block based on the derived motioninformation, wherein whether to add the prediction region mergecandidate to the merge candidate list is determined based on a result ofcomparison between motion information of the prediction region mergecandidate and motion information of a merge candidate included in themerge candidate list.
 20. A video encoding apparatus comprising an interprediction part for: deriving a merge candidate for a current block froma neighboring block of the current block; adding the derived mergecandidate to a merge candidate list; adding at least one predictionregion merge candidate derived based on motion information of theneighboring block included in a prediction region motion informationlist to the merge candidate list when a number of merge candidates addedto the merge candidate list is smaller than a first threshold valuewherein the prediction region merge candidate included in the predictionregion motion information list is obtained by determining whether theneighboring block is included in a predetermined region, wherein thepredetermined region is a merge processing area; when it is determinedthat the neighboring block is not included in the predetermined region,the prediction region merge candidate is added to the prediction regionmotion information list; and/or when it is determined that theneighboring block is included in the predetermined region, theprediction region merge candidate is not added to the prediction regionmotion information list; deriving motion information for the currentblock based on the merge candidate list; and performing motioncompensation for the current block based on the derived motioninformation, wherein whether to add the prediction region mergecandidate to the merge candidate list is determined based on a result ofcomparison between motion information of the prediction region mergecandidate and motion information of a merge candidate included in themerge candidate list.